TY  - JOUR
T1  - Measurement of the \(t\overline{t}γ\) production cross section in proton-proton collisions at \(\sqrt{s} = 8\) TeV with the ATLAS detector
JF  - Journal of High Energy Physics
N2  - The cross section of a top-quark pair produced in association with a photon is measured in proton-proton collisions at a centre-of-mass energy of \(\sqrt{s} = 8\) TeV with 20.2 fb\(^{−1}\) of data collected by the ATLAS detector at the Large Hadron Collider in 2012. The measurement is performed by selecting events that contain a photon with transverse momentum \(p_T\) > 15 GeV, an isolated lepton with large transverse momentum, large missing transverse momentum, and at least four jets, where at least one is identified as originating from a \(b\)-quark. The production cross section is measured in a fiducial region close to the selection requirements. It is found to be 139 ± 7 (stat.) ± 17 (syst.) fb, in good agreement with the theoretical prediction at next-to-leading order of 151 ± 24 fb. In addition, differential cross sections in the fiducial region are measured as a function of the transverse momentum and pseudorapidity of the photon.
KW  - High energy physics
KW  - Hadron-Hadron scattering (experiments)
KW  - Top physics
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-172399
VL  - 2017
IS  - 86
ER  - 
TY  - JOUR
T1  - Measurements of top-quark pair differential cross-sections in the lepton+jets channel in pp collisions at \( \sqrt{s}=13 \) TeV using the ATLAS detector
JF  - Journal of High Energy Physics
N2  - Measurements of differential cross-sections of top-quark pair production in fiducial phase-spaces are presented as a function of top-quark and \(t\overline{t}\) system kinematic observables in proton-proton collisions at a centre-of-mass energy of \(\sqrt{s}\) = 13 TeV. The data set corresponds to an integrated luminosity of 3.2 fb\(^{−1}\), recorded in 2015 with the ATLAS detector at the CERN Large Hadron Collider. Events with exactly one electron or muon and at least two jets in the final state are used for the measurement. Two separate selections are applied that each focus on different top-quark momentum regions, referred to as resolved and boosted topologies of the \(t\overline{t}\) final state. The measured spectra are corrected for detector effects and are compared to several Monte Carlo simulations by means of calculated \(χ^2\) and \(p\)-values.
KW  - High energy physics
KW  - Hadron-Hadron scattering (experiments)
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-172386
VL  - 2017
IS  - 191
ER  - 
TY  - JOUR
T1  - Search for supersymmetry in events with \(b\)-tagged jets and missing transverse momentum in \(pp\) collisions at \(\sqrt{s}\) = 13 TeV with the ATLAS detector
JF  - Journal of High Energy Physics
N2  - A search for the supersymmetric partners of the Standard Model bottom and top quarks is presented. The search uses 36.1 fb\(^{−1}\) of \(pp\) collision data at \(\sqrt{s}\) = 13 TeV collected by the ATLAS experiment at the Large Hadron Collider. Direct production of pairs of bottom and top squarks (\(\overline{b}_1\) and \(\overline{t}_1\)) is searched for in final states with \(b\)-tagged jets and missing transverse momentum. Distinctive selections are defined with either no charged leptons (electrons or muons) in the final state, or one charged lepton. The zero-lepton selection targets models in which the \(\overline{b}_1\) is the lightest squark and decays via \(\overline{b}_1\) → \(b\overline{χ}^0_1\), where \(\overline{χ}^0_1\) is the lightest neutralino. The one-lepton final state targets models where bottom or top squarks are produced and can decay into multiple channels, \(\overline{b}_1\) → \(b\overline{χ}^0_1\) and \(\overline{b}_1\) → \(t\overline{χ}^±_1\), or \(\overline{t}_1\) → \(t\overline{χ}^0_1\) and \(\overline{t}_1\) → \(b\overline{χ}^±_1\), where \(\overline{χ}^±_1\) is the lightest chargino and the mass difference \(m_{\overline{χ}^±_1}\) − \(m_{\overline{χ}^0_1}\) is set to 1 GeV. No excess above the expected Standard Model background is observed. Exclusion limits at 95% confidence level on the mass of third-generation squarks are derived in various supersymmetry-inspired simplified models.
KW  - High energy physics
KW  - Hadron-Hadron scattering (experiments)
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-172320
VL  - 2017
IS  - 195
ER  - 
TY  - JOUR
A1  - Maaß, Henriette
A1  - Bentmann, Hendrik
A1  - Seibel, Christoph
A1  - Tusche, Christian
A1  - Eremeev, Sergey V.
A1  - Peixoto, Thiago R.F.
A1  - Tereshchenko, Oleg E.
A1  - Kokh, Konstantin A.
A1  - Chulkov, Evgueni V.
A1  - Kirschner, Jürgen
A1  - Reinert, Friedrich
T1  - Spin-texture inversion in the giant Rashba semiconductor BiTeI
JF  - Nature Communications
N2  - Semiconductors with strong spin–orbit interaction as the underlying mechanism for the generation of spin-polarized electrons are showing potential for applications in spintronic devices. Unveiling the full spin texture in momentum space for such materials and its relation to the microscopic structure of the electronic wave functions is experimentally challenging and yet essential for exploiting spin–orbit effects for spin manipulation. Here we employ a state-of-the-art photoelectron momentum microscope with a multichannel spin filter to directly image the spin texture of the layered polar semiconductor BiTeI within the full two-dimensional momentum plane. Our experimental results, supported by relativistic ab initio calculations, demonstrate that the valence and conduction band electrons in BiTeI have spin textures of opposite chirality and of pronounced orbital dependence beyond the standard Rashba model, the latter giving rise to strong optical selection-rule effects on the photoelectron spin polarization. These observations open avenues for spin-texture manipulation by atomic-layer and charge carrier control in polar semiconductors.
KW  - applied physics
KW  - spintronics
KW  - semiconductors
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-173769
VL  - 7
ER  - 
TY  - JOUR
A1  - Chenari, Hossein Mahmoudi
A1  - Seibel, Christoph
A1  - Hauschild, Dirk
A1  - Reinert, Friedrich
A1  - Abdollahian, Hossein
T1  - Titanium Dioxide Nanoparticles: Synthesis, X-Ray Line Analysis and Chemical Composition Study
JF  - Materials Research
N2  - TiO2 nanoparticleshave been synthesized by the sol-gel method using titanium alkoxide and isopropanolas a precursor. The structural properties and chemical composition of the TiO2 nanoparticles were studied usingX-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy.The X-ray powder diffraction pattern confirms that the particles are mainly composed of the anatase phase with the preferential orientation along [101] direction. The physical parameters such as strain, stress and energy density were investigated from the Williamson- Hall (W-H) plot assuming a uniform deformation model (UDM), and uniform deformation energy density model (UDEDM). The W-H analysis shows an anisotropic nature of the strain in nanopowders. The scanning electron microscopy image shows clear TiO2 nanoparticles with particle sizes varying from 60 to 80nm. The results of mean particle size of TiO2 nanoparticles show an inter correlation with the W-H analysis and SEM results. Our X-ray photoelectron spectroscopy spectra show that nearly a complete amount of titanium has reacted to TiO2
KW  - TiO\(_2\)
KW  - Nanoparticles
KW  - X-ray analysis
KW  - SEM
KW  - XPS
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-165807
VL  - 19
IS  - 6
ER  - 
TY  - JOUR
T1  - Search for new phenomena with large jet multiplicities and missing transverse momentum using large-radius jets and flavour-tagging at ATLAS in 13 TeV \(pp\) collisions
JF  - Journal of High Energy Physics
N2  - A search is presented for particles that decay producing a large jet multiplicity and invisible particles. The event selection applies a veto on the presence of isolated electrons or muons and additional requirements on the number of \(b\)-tagged jets and the scalar sum of masses of large-radius jets. Having explored the full ATLAS 2015-2016 dataset of LHC proton-proton collisions at \(\sqrt{s}\) = 13 TeV, which corresponds to 36.1 fb\(^{−1}\) of integrated luminosity, no evidence is found for physics beyond the Standard Model. The results are interpreted in the context of simplified models inspired by R-parity-conserving and R-parity-violating supersymmetry, where gluinos are pair-produced. More generic models within the phenomenological minimal supersymmetric Standard Model are also considered.
KW  - High energy physics
KW  - Beyond Standard Model
KW  - Hadron-Hadron scattering (experiments)
KW  - Supersymmetry
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-172302
VL  - 34
ER  - 
TY  - JOUR
T1  - Measurement of the Drell-Yan triple-differential cross section in \(pp\) collisions at \(\sqrt{s}\) = 8 TeV
JF  - Journal of High Energy Physics
N2  - This paper presents a measurement of the triple-differential cross section for the Drell-Yan process \({Z/γ^*}\) → ℓ\(^+\)ℓ\(^-\) where ℓ is an electron or a muon. The measurement is performed for invariant masses of the lepton pairs, \(m_{ℓℓ}\) , between 46 and 200 GeV using a sample of 20.2 fb\(^{−1}\) of \(pp\) collisions data at a centre-of-mass energy of \(\sqrt{s}\) = 8 TeV collected by the ATLAS detector at the LHC in 2012. The data are presented in bins of invariant mass, absolute dilepton rapidity, |\(y_{ℓℓ}\)|, and the angular variable cos \(θ^*\) between the outgoing lepton and the incoming quark in the Collins-Soper frame. The measurements are performed in the range |\(y_{ℓℓ}\)| < 2.4 in the muon channel, and extended to |\(y_{ℓℓ}\)| < 3.6 in the electron channel. The cross sections are used to determine the \(Z\) boson forward-backward asymmetry as a function of |\(y_{ℓℓ}\)| and \(m_{ℓℓ}\) . The measurements achieve high-precision, below the percent level in the pole region, excluding the uncertainty in the integrated luminosity, and are in agreement with predictions. These precision data are sensitive to the parton distribution functions and the effective weak mixing angle.
KW  - high energy physics
KW  - Hadron-Hadron scattering (experiments)
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-172204
VL  - 59
ER  - 
TY  - JOUR
T1  - Analysis of the Wtb vertex from the measurement of triple-differential angular decay rates of single top quarks produced in the \(t\)-channel at \(\sqrt{s}\) = 8 TeV with the ATLAS detector
JF  - Journal or High Energy Physics
N2  - The electroweak production and subsequent decay of single top quarks in the \(t\)-channel is determined by the properties of the \({Wtb}\) vertex, which can be described by the complex parameters of an effective Lagrangian. An analysis of a triple-differential decay rate in \(t\)-channel production is used to simultaneously determine five generalised helicity fractions and phases, as well as the polarisation of the produced top quark. The complex parameters are then constrained. This analysis is based on 20.2 fb\(^{−1}\) of proton-proton collision data at a centre-of-mass energy of 8 TeV collected with the ATLAS detector at the LHC. The fraction of decays containing transversely polarised \(W\) bosons is measured to be \(f_1\) = 0.30 ± 0.05. The phase between amplitudes for transversely and longitudinally polarised \(W\) bosons recoiling against left-handed \(b\)-quarks is measured to be \(\delta\)_ = 0.002\(\pi^{+0.016\pi}_{+0.017\pi}\), giving no indication of CP violation. The fractions of longitudinal or transverse \(W\) bosons accompanied by right-handed \(b\)-quarks are also constrained. Based on these measurements, limits are placed at 95% CL on the ratio of the complex coupling parameters Re [\({g_R/V_L}\) \(\in\) [−0.12, 0.17] and Im [\({g_R/V_L}\) \(\in\) [−0.07, 0.06]. Constraints are also placed on the ratios |\({V_R}/{V_L}\)| and |\({g_L}/{V_L}\)|. In addition, the polarisation of single top quarks in the \(t\)-channel is constrained to be \(P\) > 0.72 (95% CL). None of the above measurements make assumptions about the value of any of the other parameters or couplings and all of them are in agreement with the Standard Model.
KW  - High energy physics
KW  - Electroweak interaction
KW  - Hadron-Hadron scattering (experiments)
KW  - Top physics
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-172310
VL  - 2017
IS  - 17
ER  - 
TY  - JOUR
A1  - Elsässer, S.
A1  - Schiebl, M.
A1  - Mukhin, A. A.
A1  - Balbashov, A. M.
A1  - Pimenov, A.
A1  - Geurts, J.
T1  - Impact of temperature-dependent local and global spin order in \(R\)MnO\(_3\) compounds for spin-phonon coupling and electromagnon activity
JF  - New Journal of Physics
N2  - The orthorhombic rare-earth manganite compounds \(R\)MnO\(_3\) show a global magnetic order for \(T\) < \(T\)\(_N\), and several representatives are multiferroic with a cycloidal spin ground state order for \(T\) < \(T\)\(_c\)\(_y\)\(_c\)\(_l\) < \(T\)\(_N\) \(\approx\) 40 K. We deduce from the temperature dependence of spin–phonon coupling in Raman spectroscopy for a series of \(R\)MnO\(_3\) compounds that their spin order locally persists up to about twice \(T\)\(_N\). Along the same line, our observation of the persistence of the electromagnon in GdMnO\(_3\) up to \(T\) \(\approx\) 100 K is attributed to a local cycloidal spin order for \(T\) > \(T\)\(_c\)\(_y\)\(_c\)\(_l\), in contrast to the hitherto assumed incommensurate sinusoidal phase in the intermediate temperature range. The development of the magnetization pattern can be described in terms of an order–disorder transition at \(T\)\(_c\)\(_y\)\(_c\)\(_l\) within a pseudospin model of localized spin cycloids with opposite chirality.
KW  - physics
KW  - RMnO3
KW  - multiferroics
KW  - electromagnon
KW  - Raman spectroscopy
KW  - spin-phonon coupling
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-171978
VL  - 19
ER  - 
TY  - JOUR
A1  - Franich, Robert A.
A1  - Meder, Roger
A1  - Behr, Volker C.
T1  - Dewatering Green Sapwood Using Carbon Dioxide Undergoing Cyclical Phase Change between Supercritical Fluid and Gas
JF  - Molecules
N2  - Conventional kiln drying of wood operates by the evaporation of water at elevated temperature. In the initial stage of drying, mobile water in the wood cell lumen evaporates. More slowly, water bound in the wood cell walls evaporates, requiring the breaking of hydrogen bonds between water molecules and cellulose and hemicellulose polymers in the cell wall. An alternative for wood kiln drying is a patented process for green wood dewatering through the molecular interaction of supercritical carbon dioxide with water of wood cell sap. When the system pressure is reduced to below the critical point, phase change from supercritical fluid to gas occurs with a consequent large change in CO2 volume. This results in the efficient, rapid, mechanical expulsion of liquid sap from wood. The end-point of this cyclical phase-change process is wood dewatered to the cell wall fibre saturation point. This paper describes dewatering over a range of green wood specimen sizes, from laboratory physical chemistry studies to pilot-plant trials. Magnetic resonance imaging and nuclear magnetic resonance spectroscopy were applied to study the fundamental mechanisms of the process, which were contrasted with similar studies of conventional thermal wood drying. In conclusion, opportunities and impediments towards the commercialisation of the green wood dewatering process are discussed.
KW  - supercritical CO<sub>2</sub>
KW  - phase-change
KW  - sapwood
KW  - dewatering
KW  - physical chemistry
KW  - nuclear magnetic resonance spectroscopy
KW  - magnetic resonance imaging
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-219327
SN  - 1420-3049
VL  - 25
IS  - 22
ER  - 
TY  - JOUR
A1  - Pollinger, Florian
A1  - Schmitt, Stefan
A1  - Sander, Dirk
A1  - Tian, Zhen
A1  - Kirschner, Jürgen
A1  - Vrdoljak, Pavo
A1  - Stadler, Christoph
A1  - Maier, Florian
A1  - Marchetto, Helder
A1  - Schmidt, Thomas
A1  - Schöll, Achim
A1  - Umbach, Eberhard
T1  - Nanoscale patterning, macroscopic reconstruction, and enhanced surface stress by organic adsorption on vicinal surfaces
JF  - New Journal of Physics
N2  - Self-organization is a promising method within the framework of bottom-up architectures to generate nanostructures in an efficient way. The present work demonstrates that self- organization on the length scale of a few to several tens of nanometers can be achieved by a proper combination of a large (organic) molecule and a vicinal metal surface if the local bonding of the molecule on steps is significantly stronger than that on low-index surfaces. In this case thermal annealing may lead to large mass transport of the subjacent substrate atoms such that nanometer-wide and micrometer-long molecular stripes or other patterns are being formed on high-index planes. The formation of these patterns can be controlled by the initial surface orientation and adsorbate coverage. The patterns arrange self-organized in regular arrays by repulsive mechanical interactions over long distances accompanied by a significant enhancement of surface stress. We demonstrate this effect using the planar organic molecule PTCDA as adsorbate and Ag(10 8 7) and Ag(775)surfaces as substrate. The patterns are directly observed by STM, the formation of vicinal surfaces is monitored by highresolution electron diffraction, the microscopic surface morphology changes are followed by spectromicroscopy, and the macroscopic changes of surface stress are measured by a cantilever bending method. The in situ combination of these complementary techniques provides compelling evidence for elastic interaction and a significant stress contribution to long-range order and nanopattern formation.
KW  - physics
KW  - patterning
KW  - reconstruction
KW  - surface stress
KW  - STM
KW  - SPA-LEED
KW  - vicinal surfaces
KW  - adsoption
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-171947
VL  - 19
ER  - 
TY  - JOUR
A1  - Triphan, Simon M. F.
A1  - Jobst, Bertram J.
A1  - Anjorin, Angela
A1  - Sedlaczek, Oliver
A1  - Wolf, Ursula
A1  - Terekhov, Maxim
A1  - Hoffmann, Christian
A1  - Ley, Sebastian
A1  - Düber, Christoph
A1  - Biederer, Jürgen
A1  - Kauczor, Hans-Ulrich
A1  - Jakob, Peter M.
A1  - Wielpütz, Mark O.
T1  - Reproducibility and comparison of oxygen-enhanced T\(_1\) quantification in COPD and asthma patients
JF  - PLoS ONE
N2  - T\(_1\) maps have been shown to yield useful diagnostic information on lung function in patients with chronic obstructive pulmonary disease (COPD) and asthma, both for native T\(_1\) and ΔT\(_1\), the relative reduction while breathing pure oxygen. As parameter quantification is particularly interesting for longitudinal studies, the purpose of this work was both to examine the reproducibility of lung T\(_1\) mapping and to compare T\(_1\) found in COPD and asthma patients using IRSnapShotFLASH embedded in a full MRI protocol. 12 asthma and 12 COPD patients (site 1) and further 15 COPD patients (site 2) were examined on two consecutive days. In each patient, T\(_1\) maps were acquired in 8 single breath-hold slices, breathing first room air, then pure oxygen. Maps were partitioned into 12 regions each to calculate average values. In asthma patients, the average T\(_{1,RA}\) = 1206ms (room air) was reduced to T\(_{1,O2}\) = 1141ms under oxygen conditions (ΔT\(_1\) = 5.3%, p < 5⋅10\(^{−4})\), while in COPD patients both native T\(_{1,RA}\) = 1125ms was significantly shorter (p < 10\(^{−3})\) and the relative reduction to T\(_{1,O2}\) = 1081ms on average ΔT\(_1\) = 4.2%(p < 10\(^{−5}\)). On the second day, with T\(_{1,RA}\) = 1186ms in asthma and T\(_{1,RA}\) = 1097ms in COPD, observed values were slightly shorter on average in all patient groups. ΔT\(_1\) reduction was the least repeatable parameter and varied from day to day by up to 23% in individual asthma and 30% in COPD patients. While for both patient groups T\(_1\) was below the values reported for healthy subjects, the T\(_1\) and ΔT\(_1\) found in asthmatics lies between that of the COPD group and reported values for healthy subjects, suggesting a higher blood volume fraction and better ventilation. However, it could be demonstrated that lung T\(_1\) quantification is subject to notable inter-examination variability, which here can be attributed both to remaining contrast agent from the previous day and the increased dependency of lung T\(_1\) on perfusion and thus current lung state.
KW  - Medicine
KW  - Chronic obstrusive pulmonary disease
KW  - Asthma
KW  - Oxygen
KW  - Magnetic resonance imaging
KW  - Breathing
KW  - Pulmonary imaging
KW  - Protons
KW  - Diagnostic medicine
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-171833
VL  - 12
IS  - 2
ER  - 
TY  - JOUR
A1  - Gotschy, Alexander
A1  - Bauer, Wolfgang R.
A1  - Winter, Patrick
A1  - Nordbeck, Peter
A1  - Rommel, Eberhard
A1  - Jakob, Peter M.
A1  - Herold, Volker
T1  - Local versus global aortic pulse wave velocity in early atherosclerosis: An animal study in ApoE\(^{-/-}\) mice using ultrahigh field MRI
JF  - PLoS ONE
N2  - Increased aortic stiffness is known to be associated with atherosclerosis and has a predictive value for cardiovascular events. This study aims to investigate the local distribution of early arterial stiffening due to initial atherosclerotic lesions. Therefore, global and local pulse wave velocity (PWV) were measured in ApoE\(^{-/-}\) and wild type (WT) mice using ultrahigh field MRI. For quantification of global aortic stiffness, a new multi-point transit-time (TT) method was implemented and validated to determine the global PWV in the murine aorta. Local aortic stiffness was measured by assessing the local PWV in the upper abdominal aorta, using the flow/area (QA) method. Significant differences between age matched ApoE\(^{-/-}\) and WT mice were determined for global and local PWV measurements (global PWV: ApoE\(^{-/-}\): 2.7 ±0.2m/s vs WT: 2.1±0.2m/s, P<0.03; local PWV: ApoE\(^{-/-}\): 2.9±0.2m/s vs WT: 2.2±0.2m/s, P<0.03). Within the WT mouse group, the global PWV correlated well with the local PWV in the upper abdominal aorta (R\(^2\) = 0.75, P<0.01), implying a widely uniform arterial elasticity.
In ApoE\(^{-/-}\) animals, however, no significant correlation between individual local and global PWV was present (R\(^2\) = 0.07, P = 0.53), implying a heterogeneous distribution of vascular stiffening in early atherosclerosis. The assessment of global PWV using the new multi-point TT measurement technique was validated against a pressure wire measurement in a vessel
phantom and showed excellent agreement. The experimental results demonstrate that vascular stiffening caused by early atherosclerosis is unequally distributed over the length of large vessels. This finding implies that assessing heterogeneity of arterial stiffness by multiple local measurements of PWV might be more sensitive than global PWV to identify early atherosclerotic lesions.
KW  - MRI
KW  - Atherosclerosis
KW  - Aorta
KW  - Stiffness
KW  - Measurement
KW  - Time measurement
KW  - Magnetic resonance imaging
KW  - Mouse models
KW  - Systole
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-171824
VL  - 12
IS  - 2
ER  - 
TY  - JOUR
A1  - Motyka, M.
A1  - Dyksik, M.
A1  - Ryczko, K.
A1  - Weih, R.
A1  - Dallner, M.
A1  - Höfling, S.
A1  - Kamp, M.
A1  - Sęk, G.
A1  - Misiewicz, J.
T1  - Type-II quantum wells with tensile-strained GaAsSb layers for interband cascade lasers with tailored valence band mixing
JF  - Applied Physics Letters
N2  - Optical properties of modified type II W-shaped quantum wells have been investigated with the aim to be utilized in interband cascade lasers. The results show that introducing a tensely strained GaAsSb layer, instead of a commonly used compressively strained GaInSb, allows employing the active transition involving valence band states with a significant admixture of the light holes. Theoretical predictions of multiband k.p theory have been experimentally verified by using photoluminescence and polarization dependent photoreflectance measurements. These results open a pathway for practical realization of mid-infrared lasing devices with uncommon polarization properties including, for instance, polarization-independent midinfrared light emitters.
KW  - modulation spectroscopy
KW  - semiconductors
KW  - Type-II quantum well
KW  - interband cascade laser
KW  - GaAsSb
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-189795
VL  - 108
IS  - 10
ER  - 
TY  - JOUR
A1  - Wiedenmann, J.
A1  - Bocquillon, E.
A1  - Deacon, R.S.
A1  - Hartinger, S.
A1  - Herrmann, O.
A1  - Klapwijk, T.M.
A1  - Maier, L.
A1  - Ames, C.
A1  - Brüne, C.
A1  - Gould, C.
A1  - Oiwa, A.
A1  - Ishibashi, K.
A1  - Tarucha, S.
A1  - Buhmann, H.
A1  - Molenkamp, L.W.
T1  - 4π-periodic Josephson supercurrent in HgTe-based topological Josephson junctions
JF  - Nature Communications
N2  - The Josephson effect describes the generic appearance of a supercurrent in a weak link between two superconductors. Its exact physical nature deeply influences the properties of the supercurrent. In recent years, considerable efforts have focused on the coupling of superconductors to the surface states of a three-dimensional topological insulator. In such a material, an unconventional induced p-wave superconductivity should occur, with a doublet of topologically protected gapless Andreev bound states, whose energies vary 4π-periodically with the superconducting phase difference across the junction. In this article, we report the observation of an anomalous response to rf irradiation in a Josephson junction made of a HgTe weak link. The response is understood as due to a 4π-periodic contribution to the supercurrent, and its amplitude is compatible with the expected contribution of a gapless Andreev doublet. Our work opens the way to more elaborate experiments to investigate the induced superconductivity in a three-dimensional insulator.
KW  - Josephson effect
KW  - supercurrent
KW  - superconductors
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-175353
VL  - 7
ER  - 
TY  - JOUR
A1  - Hsu, Pin-Jui
A1  - Kügel, Jens
A1  - Kemmer, Jeannette
A1  - Toldin, Francesco Parisen
A1  - Mauerer, Tobias
A1  - Vogt, Matthias
A1  - Assaad, Fakher
A1  - Bode, Matthias
T1  - Coexistence of charge and ferromagnetic order in fcc Fe
JF  - Nature Communications
N2  - Phase coexistence phenomena have been intensively studied in strongly correlated materials where several ordered states simultaneously occur or compete. Material properties critically depend on external parameters and boundary conditions, where tiny changes result in qualitatively different ground states. However, up to date, phase coexistence phenomena have exclusively been reported for complex compounds composed of multiple elements. Here we show that charge- and magnetically ordered states coexist in double-layer Fe/Rh(001). Scanning tunnelling microscopy and spectroscopy measurements reveal periodic charge-order stripes below a temperature of 130 K. Close to liquid helium temperature, they are superimposed by ferromagnetic domains as observed by spin-polarized scanning tunnelling microscopy. Temperature-dependent measurements reveal a pronounced cross-talk between charge and spin order at the ferromagnetic ordering temperature about 70 K, which is successfully modelled within an effective Ginzburg–Landau ansatz including sixth-order terms. Our results show that subtle balance between structural modifications can lead to competing ordering phenomena.
KW  - ferromagnetism
KW  - phase transitions and critical phenomena
KW  - coexistence
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-173969
VL  - 7
ER  - 
TY  - JOUR
A1  - Sessi, Paolo
A1  - Biswas, Rudro R.
A1  - Bathon, Thomas
A1  - Storz, Oliver
A1  - Wilfert, Stefan
A1  - Barla, Alessandro
A1  - Kokh, Konstantin A.
A1  - Tereshchenko, Oleg E.
A1  - Fauth, Kai
A1  - Bode, Matthias
A1  - Balatsky, Alexander V.
T1  - Dual nature of magnetic dopants and competing trends in topological insulators
JF  - Nature Communications
N2  - Topological insulators interacting with magnetic impurities have been reported to host several unconventional effects. These phenomena are described within the framework of gapping Dirac quasiparticles due to broken time-reversal symmetry. However, the overwhelming majority of studies demonstrate the presence of a finite density of states near the Dirac point even once topological insulators become magnetic. Here, we map the response of topological states to magnetic impurities at the atomic scale. We demonstrate that magnetic order and gapless states can coexist. We show how this is the result of the delicate balance between two opposite trends, that is, gap opening and emergence of a Dirac node impurity band, both induced by the magnetic dopants. Our results evidence a more intricate and rich scenario with respect to the once generally assumed, showing how different electronic and magnetic states may be generated and controlled in this fascinating class of materials.
KW  - magnetic properties and materials
KW  - topological insulators
KW  - magnetic dopants
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-172704
VL  - 7
ER  - 
TY  - JOUR
A1  - Lundt, Nils
A1  - Klembt, Sebastian
A1  - Cherotchenko, Evgeniia
A1  - Betzold, Simon
A1  - Iff, Oliver
A1  - Nalitov, Anton V.
A1  - Klaas, Martin
A1  - Dietrich, Christof P.
A1  - Kavokin, Alexey V.
A1  - Höfling, Sven
A1  - Schneider, Christian
T1  - Room-temperature Tamm-plasmon exciton-polaritons with a WSe\(_{2}\) monolayer
JF  - Nature Communications
N2  - Solid-state cavity quantum electrodynamics is a rapidly advancing field, which explores the frontiers of light–matter coupling. Metal-based approaches are of particular interest in this field, as they carry the potential to squeeze optical modes to spaces significantly below the diffraction limit. Transition metal dichalcogenides are ideally suited as the active material in cavity quantum electrodynamics, as they interact strongly with light at the ultimate monolayer limit. Here, we implement a Tamm-plasmon-polariton structure and study the coupling to a monolayer of WSe\(_{2}\), hosting highly stable excitons. Exciton-polariton formation at room temperature is manifested in the characteristic energy–momentum dispersion relation studied in photoluminescence, featuring an anti-crossing between the exciton and photon modes with a Rabi-splitting of 23.5 meV. Creating polaritonic quasiparticles in monolithic, compact architectures with atomic monolayers under ambient conditions is a crucial step towards the exploration of nonlinearities, macroscopic coherence and advanced spinor physics with novel, low-mass bosons.
KW  - optics and photonics
KW  - two-dimensional materials
KW  - electronic properties and materials
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-169470
VL  - 7
ER  - 
TY  - JOUR
A1  - He, Yu-Ming
A1  - Iff, Oliver
A1  - Lundt, Nils
A1  - Baumann, Vasilij
A1  - Davanco, Marcelo
A1  - Srinivasan, Kartik
A1  - Höfling, Sven
A1  - Schneider, Christian
T1  - Cascaded emission of single photons from the biexciton in monolayered WSe\(_{2}\)
JF  - Nature Communications
N2  - Monolayers of transition metal dichalcogenide materials emerged as a new material class to study excitonic effects in solid state, as they benefit from enormous Coulomb correlations between electrons and holes. Especially in WSe\(_{2}\), sharp emission features have been observed at cryogenic temperatures, which act as single photon sources. Tight exciton localization has been assumed to induce an anharmonic excitation spectrum; however, the evidence of the hypothesis, namely the demonstration of a localized biexciton, is elusive. Here we unambiguously demonstrate the existence of a localized biexciton in a monolayer of WSe\(_{2}\), which triggers an emission cascade of single photons. The biexciton is identified by its time-resolved photoluminescence, superlinearity and distinct polarization in micro-photoluminescence experiments. We evidence the cascaded nature of the emission process in a cross-correlation experiment, which yields a strong bunching behaviour. Our work paves the way to a new generation of quantum optics experiments with two-dimensional semiconductors.
KW  - lasers
KW  - LED
KW  - quantum dots
KW  - light sources
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-169363
VL  - 7
ER  - 
TY  - JOUR
A1  - Kurz, Felix T.
A1  - Kampf, Thomas
A1  - Buschle, Lukas R.
A1  - Schlemmer, Heinz-Peter
A1  - Bendszus, Martin
A1  - Heiland, Sabine
A1  - Ziener, Christian H.
T1  - Generalized moment analysis of magnetic field correlations for accumulations of spherical and cylindrical magnetic perturbers
JF  - Frontiers in Physics
N2  - In biological tissue, an accumulation of similarly shaped objects with a susceptibility difference to the surrounding tissue generates a local distortion of the external magnetic field in magnetic resonance imaging. It induces stochastic field fluctuations that characteristically influence proton spin dephasing in the vicinity of these magnetic perturbers. The magnetic field correlation that is associated with such local magnetic field inhomogeneities can be expressed in the form of a dynamic frequency autocorrelation function that is related to the time evolution of the measured magnetization. Here, an eigenfunction expansion for two simple magnetic perturber shapes, that of spheres and cylinders, is considered for restricted spin diffusion in a simple model geometry. Then, the concept of generalized moment analysis, an approximation technique that is applied in the study of (non-)reactive processes that involve Brownian motion, allows deriving analytical expressions of the correlation function for different exponential decay forms. Results for the biexponential decay for both spherical and cylindrical magnetized objects are derived and compared with the frequently used (less accurate) monoexponential decay forms. They are in asymptotic agreement with the numerically exact value of the correlation function for long and short times.
KW  - magnetized sphere/cylinder
KW  - magnetic susceptibility
KW  - correlation function
KW  - diffusion
KW  - magnetic resonance imaging
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-190604
SN  - 2296-424X
VL  - 4
ER  - 
TY  - JOUR
A1  - Hattori, Yohei
A1  - Michail, Evripidis
A1  - Schmiedel, Alexander
A1  - Moos, Michael
A1  - Holzapfel, Marco
A1  - Krummenacher, Ivo
A1  - Braunschweig, Holger
A1  - Müller, Ulrich
A1  - Pflaum, Jens
A1  - Lambert, Christoph
T1  - Luminescent Mono-, Di-, and Tri-radicals: Bridging Polychlorinated Triarylmethyl Radicals by Triarylamines and Triarylboranes
JF  - Chemistry - A European Journal
N2  - Up to three polychlorinated pyridyldiphenylmethyl radicals bridged by a triphenylamine carrying electron withdrawing (CN), neutral (Me), or donating (OMe) groups were synthesized and analogous radicals bridged by tris(2,6‐dimethylphenyl)borane were prepared for comparison. All compounds were as stable as common closed‐shell organic compounds and showed significant fluorescence upon excitation. Electronic, magnetic, absorption, and emission properties were examined in detail, and experimental results were interpreted using DFT calculations. Oxidation potentials, absorption and emission energies could be tuned depending on the electron density of the bridges. The triphenylamine bridges mediated intramolecular weak antiferromagnetic interactions between the radical spins, and the energy difference between the high spin and low spin states was determined by temperature dependent ESR spectroscopy and DFT calculations. The fluorescent properties of all radicals were examined in detail and revealed no difference for high and low spin states which facilitates application of these dyes in two‐photon absorption spectroscopy and OLED devices.
KW  - density functional calculations
KW  - fluorescence
KW  - NIR OLED
KW  - radical
KW  - two-photon absorption
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-208162
VL  - 25
IS  - 68
ER  - 
TY  - JOUR
A1  - Nitsche, Wolfgang H.
A1  - Kim, Na Young
A1  - Roumpos, Georgios
A1  - Schneider, Christian
A1  - Höfling, Sven
A1  - Forchel, Alfred
A1  - Yamamoto, Yoshihisa
T1  - Spatial correlation of two-dimensional bosonic multimode condensates
JF  - Physical Review A
N2  - The Berezinskii-Kosterlitz-Thouless (BKT) theorem predicts that two-dimensional bosonic condensates exhibit quasi-long-range order which is characterized by a slow decay of the spatial coherence. However previous measurements on exciton-polariton condensates revealed that their spatial coherence can decay faster than allowed under the BKT theory, and different theoretical explanations have already been proposed. Through theoretical and experimental study of exciton-polariton condensates, we show that the fast decay of the coherence can be explained through the simultaneous presence of multiple modes in the condensate.
KW  - Exciton-polariton condensate
KW  - Long-range order
KW  - Microcavity
KW  - Vortices
KW  - Systems
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-188897
VL  - 93
IS  - 5
ER  - 
TY  - JOUR
A1  - Dyksik, M.
A1  - Motyka, M.
A1  - Kurka, M.
A1  - Ryczo, K.
A1  - Dallner, M.
A1  - Höfling, S.
A1  - Kamp, M.
A1  - Sęk, G.
A1  - Misiwicz, J.
T1  - Photoluminescence quenching mechanisms in type IIInAs/GaInSb QWs on InAs substrates
JF  - Optical and Quantum Electronics
N2  - Optical properties of AlSb/InAs/GaInSb/InAs/AlSb quantum wells (QWs) grown on an InAs substrate were investigated from the point of view of room temperature emission in the mid- and long-wavelength infrared ranges. By means of two independent techniques of optical spectroscopy, photoreflectance and temperature-dependent photoluminescence, it was proven that the main process limiting the performance of such InAs substrate-based type II structures is related to the escape of carriers from the hole ground state of the QW. Two nonradiative recombination channels were identified. The main process was attributed to holes tunneling to the valence band of the GaAsSb spacing layer and the second one with trapping of holes by native defects located in the same layer.
KW  - Interband cascade lasers
KW  - Quantum wells
KW  - MU-M
KW  - Fourier-transform spectroscopy
KW  - Mid-infrared photoluminescence
KW  - Type II quantum wells
KW  - Localized states
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-204672
VL  - 48
IS  - 401
ER  - 
TY  - JOUR
A1  - Laiho, K.
A1  - Pressl, B.
A1  - Schlager, A.
A1  - Suchomel, H.
A1  - Kamp, M.
A1  - Höfling, S.
A1  - Schneider, C.
A1  - Weihs, G.
T1  - Uncovering dispersion properties in semiconductor waveguides to study photon-pair generation
JF  - Nanotechnology
N2  - We investigate the dispersion properties of ridge Bragg-reflection waveguides to deduce their phasematching characteristics. These are crucial for exploiting them as sources of parametric down-conversion (PDC). In order to estimate the phasematching bandwidth we first determine the group refractive indices of the interacting modes via Fabry-Perot experiments in two distant wavelength regions. Second, by measuring the spectra of the emitted PDC photons, we gain access to their group index dispersion. Our results offer a simple approach for determining the PDC process parameters in the spectral domain, and provide important feedback for designing such sources, especially in the broadband case.
KW  - Parametric down-conversion
KW  - Entanglement
KW  - CHIP
KW  - PUMP
KW  - Bragg-reflection waveguide
KW  - Information
KW  - phasematching
KW  - group refractive index
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-187025
VL  - 27
IS  - 43
ER  - 
TY  - JOUR
A1  - Munz, Eberhard
A1  - Jakob, Peter M.
A1  - Borisjuk, Ljudmilla
T1  - The potential of nuclear magnetic resonance to track lipids in planta
JF  - Biochimie
N2  - Nuclear Magnetic Resonance (NMR) provides a highly flexible platform for non invasive analysis and imaging biological samples, since the manipulation of nuclear spin allows the tailoring of experiments to maximize the informativeness of the data. MRI is capable of visualizing a holistic picture of the lipid storage in living plant/seed. This review has sought to explain how the technology can be used to acquire functional and physiological data from plant samples, and how to exploit it to characterize lipid deposition in vivo. At the same time, we have referred to the current limitations of NMR technology as applied to plants, and in particular of the difficulty of transferring methodologies optimized for animal/medical subjects to plant ones. A forward look into likely developments in the field is included, anticipating its key future role in the study of living plant.
KW  - coconut cocos-nucifera
KW  - H-1-NMR spectroscopy
KW  - NMR-spectroscopy
KW  - camelina-sativa
KW  - high-throughput
KW  - oil storage
KW  - seeds
KW  - accumulation
KW  - field
KW  - metabolism
KW  - NMR
KW  - Lipid
KW  - MRI
KW  - CSI
KW  - Plants
KW  - Seeds
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-186828
VL  - 130
ER  - 
TY  - JOUR
A1  - Vogel, Patrick
A1  - Markert, Jonathan
A1  - Rückert, Martin A.
A1  - Herz, Stefan
A1  - Keßler, Benedikt
A1  - Dremel, Kilian
A1  - Althoff, Daniel
A1  - Weber, Matthias
A1  - Buzug, Thorsten M.
A1  - Bley, Thorsten A.
A1  - Kullmann, Walter H.
A1  - Hanke, Randolf
A1  - Zabler, Simon
A1  - Behr, Volker C.
T1  - Magnetic Particle Imaging meets computed tomography: first simultaneous imaging
JF  - Scientific Reports
N2  - Magnetic Particle Imaging (MPI) is a promising new tomographic modality for fast as well as three-dimensional visualization of magnetic material. For anatomical or structural information an additional imaging modality such as computed tomography (CT) is required. In this paper, the first hybrid MPI-CT scanner for multimodal imaging providing simultaneous data acquisition is presented.
KW  - Applied physics
KW  - Biomedical engineering
KW  - Imaging techniques
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-202501
VL  - 9
ER  - 
TY  - JOUR
A1  - Herold, Volker
A1  - Kampf, Thomas
A1  - Jakob, Peter Michael
T1  - Dynamic magnetic resonance scattering
JF  - Communications Physics
N2  - Dynamic light scattering is a popular technique to determine the size distribution of small particles in the sub micrometer region. It operates in reciprocal space, by analyzing the signal fluctuations with the photon auto correlation function. Equally, pulsed field gradient magnetic resonance is a technique generating data in the reciprocal space of the density distribution of an object. Here we show the feasibility of employing a magnetic resonance imaging system as a dynamic scattering device similar to dynamic light scattering appliances. By acquiring a time series of single data points from reciprocal space, analogue to dynamic light scattering, we demonstrate the examination of motion patterns of microscopic particles. This method allows the examination of particle dynamics significantly below the spatial resolution of magnetic resonance imaging. It is not limited by relaxation times and covers a wide field of applications for particle or cell motion in opaque media.
KW  - Characterization and analytical techniques
KW  - Imaging techniques
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-201091
VL  - 2
ER  - 
TY  - JOUR
A1  - Winter, Patrick
A1  - Andelovic, Kristina
A1  - Kampf, Thomas
A1  - Gutjahr, Fabian Tobias
A1  - Heidenreich, Julius
A1  - Zernecke, Alma
A1  - Bauer, Wolfgang Rudolf
A1  - Jakob, Peter Michael
A1  - Herold, Volker
T1  - Fast self-navigated wall shear stress measurements in the murine aortic archusing radial 4D-phase contrast cardiovascular magnetic resonance at 17.6 T
JF  - Journal of Cardiovascular Magnetic Resonance
N2  - Purpose
4D flow cardiovascular magnetic resonance (CMR) and the assessment of wall shear stress (WSS) are non-invasive tools to study cardiovascular risks in vivo. Major limitations of conventional triggered methods are the long measurement times needed for high-resolution data sets and the necessity of stable electrocardiographic (ECG) triggering. In this work an ECG-free retrospectively synchronized method is presented that enables accelerated high-resolution measurements of 4D flow and WSS in the aortic arch of mice.

Methods
4D flow and WSS were measured in the aortic arch of 12-week-old wildtype C57BL/6 J mice (n = 7) with a radial 4D-phase-contrast (PC)-CMR sequence, which was validated in a flow phantom. Cardiac and respiratory motion signals were extracted from the radial CMR signal and were used for the reconstruction of 4D-flow data. Rigid motion correction and a first order B0 correction was used to improve the robustness of magnitude and velocity data.

The aortic lumen was segmented semi-automatically. Temporally averaged and time-resolved WSS and oscillatory shear index (OSI) were calculated from the spatial velocity gradients at the lumen surface at 14 locations along the aortic arch. Reproducibility was tested in 3 animals and the influence of subsampling was investigated.

Results
Volume flow, cross-sectional areas, WSS and the OSI were determined in a measurement time of only 32 min. Longitudinal and circumferential WSS and radial stress were assessed at 14 analysis planes along the aortic arch. The average longitudinal, circumferential and radial stress values were 1.52 ± 0.29 N/m2, 0.28 ± 0.24 N/m2 and − 0.21 ± 0.19 N/m2, respectively. Good reproducibility of WSS values was observed.

Conclusion
This work presents a robust measurement of 4D flow and WSS in mice without the need of ECG trigger signals. The retrospective approach provides fast flow quantification within 35 min and a flexible reconstruction framework.
KW  - 4D flow
KW  - WSS
KW  - OSI
KW  - Self-navigation
KW  - Mouse
KW  - Aortic arch
Y1  - 2019
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-201120
VL  - 21
ER  - 
TY  - JOUR
A1  - Dittmann, Jonas
A1  - Balles, Andreas
A1  - Zabler, Simon
T1  - Optimization based evaluation of grating interferometric phase stepping series and analysis of mechanical setup instabilities
JF  - Journal of Imaging
N2  - The diffraction contrast modalities accessible by X-ray grating interferometers are not imaged directly but have to be inferred from sine-like signal variations occurring in a series of images acquired at varying relative positions of the interferometer’s gratings. The absolute spatial translations involved in the acquisition of these phase stepping series usually lie in the range of only a few hundred nanometers, wherefore positioning errors as small as 10 nm will already translate into signal uncertainties of 1–10% in the final images if not accounted for. Classically, the relative grating positions in the phase stepping series are considered input parameters to the analysis and are, for the Fast Fourier Transform that is typically employed, required to be equidistantly distributed over multiples of the gratings’ period. In the following, a fast converging optimization scheme is presented simultaneously determining the phase stepping curves’ parameters as well as the actually performed motions of the stepped grating, including also erroneous rotational motions which are commonly neglected. While the correction of solely the translational errors along the stepping direction is found to be sufficient with regard to the reduction of image artifacts, the possibility to also detect minute rotations about all axes proves to be a valuable tool for system calibration and monitoring. The simplicity of the provided algorithm, in particular when only considering translational errors, makes it well suitable as a standard evaluation procedure also for large image series.
KW  - X-ray imaging
KW  - Talbot–Lau interferometer
KW  - grating interferometer
KW  - phase contrast imaging
KW  - darkfield imaging
KW  - phase stepping
KW  - optimization
Y1  - 2018
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-197723
SN  - 2313-433X
VL  - 4
IS  - 6
ER  - 
TY  - JOUR
A1  - Fornari, C. I.
A1  - Rappl, P. H. O.
A1  - Morelhao, S. L.
A1  - Peixoto, T. R. F.
A1  - Bentmann, H.
A1  - Reinert, F.
A1  - Abramof, E.
T1  - Preservation of pristine Bi\(_2\)Te\(_3\) thin film topological insulator surface after ex situ mechanical removal of Te capping layer
JF  - APL Materials
N2  - Ex situ analyses on topological insulator films require protection against surface contamination during air exposure. This work reports on a technique that combines deposition of protective capping just after epitaxial growth and its mechanical removal inside ultra-high vacuum systems. This method was applied to Bi2Te3 films with thickness varying from 8 to 170 nm. Contrarily to other methods, this technique does not require any sputtering or thermal annealing setups installed inside the analyzing system and preserves both film thickness and surface characteristics. These results suggest that the technique presented here can be expanded to other topological insulator materials.
KW  - Insulator surfaces
KW  - Atomic force microscopy
KW  - Insulating thin films
KW  - Molecular beam epitaxy
KW  - Surface states
KW  - Vacuum chambers
KW  - Thin film growth
KW  - Sputter deposition
KW  - Epitaxy
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-164468
VL  - 4
ER  - 
TY  - JOUR
A1  - Deacon, R. S.
A1  - Wiedenmann, J.
A1  - Bocquillon, E.
A1  - Domínguez, F.
A1  - Klapwijk, T. M.
A1  - Leubner, P.
A1  - Brüne, C.
A1  - Hankiewicz, E. M.
A1  - Tarucha, S.
A1  - Ishibashi, K.
A1  - Buhmann, H.
A1  - Molenkamp, L. W.
T1  - Josephson Radiation from Gapless Andreev Bound States in HgTe-Based Topological Junctions
JF  - Physical Review X
N2  - Frequency analysis of the rf emission of oscillating Josephson supercurrent is a powerful passive way of probing properties of topological Josephson junctions. In particular, measurements of the Josephson emission enable the detection of topological gapless Andreev bound states that give rise to emission at half the Josephson frequency f\(_{J}\) rather than conventional emission at f\(_{J}\). Here, we report direct measurement of rf emission spectra on Josephson junctions made of HgTe-based gate-tunable topological weak links. The emission spectra exhibit a clear signal at half the Josephson frequency f\(_{J}\)/2. The linewidths of emission lines indicate a coherence time of 0.3–4 ns for the f\(_{J}\)/2 line, much shorter than for the f\(_{J}\) line (3–4 ns). These observations strongly point towards the presence of topological gapless Andreev bound states and pave the way for a future HgTe-based platform for topological quantum computation.
KW  - condensed matter physics
KW  - Josephson junctions
KW  - topological materials
KW  - gapless Andreev bound states
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-170969
VL  - 7
IS  - 021011
ER  - 
TY  - JOUR
A1  - Shamim, Saquib
A1  - Mahapatra, S.
A1  - Scappucci, G.
A1  - Klesse, W. M.
A1  - Simmons, M. Y.
A1  - Ghosh, Arindam
T1  - Dephasing rates for weak localization and universal conductance fluctuations in two dimensional Si: P and Ge: P δ-layers
JF  - Scientific Reports
N2  - We report quantum transport measurements on two dimensional (2D) Si:P and Ge:P δ-layers and compare the inelastic scattering rates relevant for weak localization (WL) and universal conductance fluctuations (UCF) for devices of various doping densities (0.3–2.5 × 10\(^{18}\)m\(^{−2}\)) at low temperatures (0.3–4.2 K). The phase breaking rate extracted experimentally from measurements of WL correction to conductivity and UCF agree well with each other within the entire temperature range. This establishes that WL and UCF, being the outcome of quantum interference phenomena, are governed by the same dephasing rate.
KW  - two-dimensional materials
KW  - quantum information
KW  - electronic properties and materials
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-170934
VL  - 7
IS  - 46670
ER  - 
TY  - JOUR
A1  - Dziom, V.
A1  - Shuvaev, A.
A1  - Pimenov, A.
A1  - Astakhov, G.V.
A1  - Ames, C.
A1  - Bendias, K.
A1  - Böttcher, J.
A1  - Tkachov, G.
A1  - Hankiewicz, E.M.
A1  - Brüne, C.
A1  - Buhmann, H.
A1  - Molenkamp, L.W.
T1  - Observation of the universal magnetoelectric effect in a 3D topological insulator
JF  - Nature Communications
N2  - The electrodynamics of topological insulators (TIs) is described by modified Maxwell’s equations, which contain additional terms that couple an electric field to a magnetization and a magnetic field to a polarization of the medium, such that the coupling coefficient is quantized in odd multiples of α/4π per surface. Here we report on the observation of this so-called topological magnetoelectric effect. We use monochromatic terahertz (THz) spectroscopy of TI structures equipped with a semitransparent gate to selectively address surface states. In high external magnetic fields, we observe a universal Faraday rotation angle equal to the fine structure constant α=e\(^{2}\)/2E\(_{0}\)hc (in SI units) when a linearly polarized THz radiation of a certain frequency passes through the two surfaces of a strained HgTe 3D TI. These experiments give insight into axion electrodynamics of TIs and may potentially be used for a metrological definition of the three basic physical constants.
KW  - topological matter
KW  - infrared spectroscopy
KW  - topological insulators
KW  - topological magnetoelectric effect
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-170875
VL  - 8
IS  - 15197
ER  - 
TY  - JOUR
A1  - Straßer, Marion
A1  - Schrauth, Joachim H. X.
A1  - Dembski, Sofia
A1  - Haddad, Daniel
A1  - Ahrens, Bernd
A1  - Schweizer, Stefan
A1  - Christ, Bastian
A1  - Cubukova, Alevtina
A1  - Metzger, Marco
A1  - Walles, Heike
A1  - Jakob, Peter M.
A1  - Sextl, Gerhard
T1  - Calcium fluoride based multifunctional nanoparticles for multimodal imaging
JF  - Beilstein Journal of Nanotechnology
N2  - New multifunctional nanoparticles (NPs) that can be used as contrast agents (CA) in different imaging techniques, such as photoluminescence (PL) microscopy and magnetic resonance imaging (MRI), open new possibilities for medical imaging, e.g., in the fields of diagnostics or tissue characterization in regenerative medicine. The focus of this study is on the synthesis and characterization of CaF\(_{2}\):(Tb\(^{3+}\),Gd\(^{3+}\)) NPs. Fabricated in a wet-chemical procedure, the spherical NPs with a diameter of 5–10 nm show a crystalline structure. Simultaneous doping of the NPs with different lanthanide ions, leading to paramagnetism and fluorescence, makes them suitable for MR and PL imaging. Owing to the Gd\(^{3+}\) ions on the surface, the NPs reduce the MR T\(_{1}\) relaxation time constant as a function of their concentration. Thus, the NPs can be used as a MRI CA with a mean relaxivity of about r = 0.471 mL·mg\(^{−1}\)·s\(^{−1}\). Repeated MRI examinations of four different batches prove the reproducibility of the NP synthesis and determine the long-term stability of the CAs. No cytotoxicity of NP concentrations between 0.5 and 1 mg·mL\(^{−1}\) was observed after exposure to human dermal fibroblasts over 24 h. Overall this study shows, that the CaF\(_{2}\):(Tb\(^{3+}\),Gd\(^{3+}\)) NPs are suitable for medical imaging.
KW  - calcium fluoride nanoparticles
KW  - magnetic resonance imaging (MRI)
KW  - multifunctional nanoparticles
KW  - multimodal imaging
KW  - photoluminescence
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-170657
VL  - 8
ER  - 
TY  - JOUR
A1  - Biedermann, Benedikt
A1  - Bräuer, Stephan
A1  - Denner, Ansgar
A1  - Pellen, Mathieu
A1  - Schumann, Steffen
A1  - Thompson, Jennifer M.
T1  - Automation of NLO QCD and EW corrections with SHERPA and RECOLA
JF  - European Physical Journal C
N2  - This publication presents the combination of the one-loop matrix-element generator Recola with the multipurpose Monte Carlo program Sherpa. Since both programs are highly automated, the resulting Sherpa +Recola framework allows for the computation of – in principle – any Standard Model process at both NLO QCD and EW accuracy. To illustrate this, three representative LHC processes have been computed at NLO QCD and EW: vector-boson production in association with jets, off-shell Z-boson pair production, and the production of a top-quark pair in association with a Higgs boson. In addition to fixed-order computations, when considering QCD corrections, all functionalities of Sherpa, i.e. particle decays, QCD parton showers, hadronisation, underlying events, etc. can be used in combination with Recola. This is demonstrated by the merging and matching of one-loop QCD matrix elements for Drell–Yan production in association with jets to the parton shower. The implementation is fully automatised, thus making it a perfect tool for both experimentalists and theorists who want to use state-of-the-art predictions at NLO accuracy.
KW  - RECOLA
KW  - SHERPA
KW  - NLO QCD
KW  - EW
KW  - Higgs boson
KW  - Large Hadron Collider
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-170615
VL  - 77
IS  - 492
ER  - 
TY  - JOUR
A1  - Wurdack, Matthias
A1  - Lundt, Nils
A1  - Klaas, Martin
A1  - Baumann, Vasilij
A1  - Kavokin, Alexey V.
A1  - Höfling, Sven
A1  - Schneider, Christian
T1  - Observation of hybrid Tamm-plasmon exciton-polaritons with GaAs quantum wells and a MoSe\(_{2}\) monolayer
JF  - Nature Communications
N2  - Strong light matter coupling between excitons and microcavity photons, as described in the framework of cavity quantum electrodynamics, leads to the hybridization of light and matter excitations. The regime of collective strong coupling arises, when various excitations from different host media are strongly coupled to the same optical resonance. This leads to a well-controllable admixture of various matter components in three hybrid polariton modes. Here, we study a cavity device with four embedded GaAs quantum wells hosting excitons that are spectrally matched to the A-valley exciton resonance of a MoSe\(_{2}\) monolayer. The formation of hybrid polariton modes is evidenced in momentum resolved photoluminescence and reflectivity studies. We describe the energy and k-vector distribution of exciton-polaritons along the hybrid modes by a thermodynamic model, which yields a very good agreement with the experiment.
KW  - two-dimensional materials
KW  - microresonators
KW  - nanophotonics and plasmonics
KW  - cavity device
KW  - strong coupling
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-170480
VL  - 8
IS  - 259
ER  - 
TY  - JOUR
A1  - Min, Chul-Hee
A1  - Goth, F.
A1  - Lutz, P.
A1  - Bentmann, H.
A1  - Kang, B.Y.
A1  - Cho, B.K.
A1  - Werner, J.
A1  - Chen, K.-S.
A1  - Assaad, F.
A1  - Reinert, F.
T1  - Matching DMFT calculations with photoemission spectra of heavy fermion insulators: universal properties of the near-gap spectra of SmB\(_{6}\)
JF  - Scientific Reports
N2  - Paramagnetic heavy fermion insulators consist of fully occupied quasiparticle bands inherent to Fermi liquid theory. The gap emergence below a characteristic temperature is the ultimate sign of coherence for a many-body system, which in addition can induce a non-trivial band topology. Here, we demonstrate a simple and efficient method to compare a model study and an experimental result for heavy fermion insulators. The temperature dependence of the gap formation in both local moment and mixed valence regimes is captured within the dynamical mean field (DMFT) approximation to the periodic Anderson model (PAM). Using the topological coherence temperature as the scaling factor and choosing the input parameter set within the mixed valence regime, we can unambiguously link the theoretical energy scales to the experimental ones. As a particularly important result, we find improved consistency between the scaled DMFT density of states and the photoemission near-gap spectra of samarium hexaboride (SmB\(_{6}\)).
KW  - SmB\(_{6}\)
KW  - heavy fermion insulators
KW  - dynamical mean field
KW  - samarium hexaboride
KW  - near-gap spectra
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-170328
VL  - 7
IS  - 11980
ER  - 
TY  - JOUR
A1  - Dietrich, Christof P.
A1  - Steude, Anja
A1  - Tropf, Laura
A1  - Schubert, Marcel
A1  - Kronenberg, Nils M.
A1  - Ostermann, Kai
A1  - Höfling, Sven
A1  - Gather, Malte C.
T1  - An exciton-polariton laser based on biologically produced fluorescent protein
JF  - Science Advances
N2  - Under adequate conditions, cavity polaritons form a macroscopic coherent quantum state, known as polariton condensate. Compared to Wannier-Mott excitons in inorganic semiconductors, the localized Frenkel excitons in organic emitter materials show weaker interaction with each other but stronger coupling to light, which recently enabled the first realization of a polariton condensate at room temperature. However, this required ultrafast optical pumping, which limits the applications of organic polariton condensates. We demonstrate room temperature polariton condensates of cavity polaritons in simple laminated microcavities filled with biologically produced enhanced green fluorescent protein (eGFP). The unique molecular structure of eGFP prevents exciton annihilation even at high excitation densities, thus facilitating polariton condensation under conventional nanosecond pumping. Condensation is clearly evidenced by a distinct threshold, an interaction-induced blueshift of the condensate, long-range coherence, and the presence of a second threshold at higher excitation density that is associated with the onset of photon lasing.
KW  - polarition condensate
KW  - enhanced green fluorescent protein
KW  - photon lasing
KW  - quantum physics
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-171305
VL  - 2
IS  - 8
ER  - 
TY  - JOUR
A1  - Lousada, Cláudio M.
A1  - Soroka, Inna L.
A1  - Yagodzinskyy, Yuriy
A1  - Tarakina, Nadezda V.
A1  - Todoshchenko, Olga
A1  - Hänninen, Hannu
A1  - Korzhavyi, Pavel A.
A1  - Jonsson, Mats
T1  - Gamma radiation induces hydrogen absorption by copper in water
JF  - Scientific Reports
N2  - One of the most intricate issues of nuclear power is the long-term safety of repositories for radioactive waste. These repositories can have an impact on future generations for a period of time orders of magnitude longer than any known civilization. Several countries have considered copper as an outer corrosion barrier for canisters containing spent nuclear fuel. Among the many processes that must be considered in the safety assessments, radiation induced processes constitute a key-component. Here we show that copper metal immersed in water uptakes considerable amounts of hydrogen when exposed to γ-radiation. Additionally we show that the amount of hydrogen absorbed by copper depends on the total dose of radiation. At a dose of 69 kGy the uptake of hydrogen by metallic copper is 7 orders of magnitude higher than when the absorption is driven by H\(_{2}\)(g) at a pressure of 1 atm in a non-irradiated dry system. Moreover, irradiation of copper in water causes corrosion of the metal and the formation of a variety of surface cavities, nanoparticle deposits, and islands of needle-shaped crystals. Hence, radiation enhanced uptake of hydrogen by spent nuclear fuel encapsulating materials should be taken into account in the safety assessments of nuclear waste repositories.
KW  - gamma radiation
KW  - radioactive waste
KW  - nuclear power
KW  - repositories
KW  - safety
KW  - copper
KW  - water
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-167730
VL  - 6
IS  - 24234
ER  - 
TY  - JOUR
A1  - Audehm, P.
A1  - Schmidt, M.
A1  - Brück, S.
A1  - Tietze, T.
A1  - Gräfe, J.
A1  - Macke, S.
A1  - Schütz, G.
A1  - Goering, E.
T1  - Pinned orbital moments - A new contribution to magnetic anisotropy
JF  - Scientific Reports
N2  - Reduced dimensionality and symmetry breaking at interfaces lead to unusual local magnetic configurations, such as glassy behavior, frustration or increased anisotropy. The interface between a ferromagnet and an antiferromagnet is such an example for enhanced symmetry breaking. Here we present detailed X-ray magnetic circular dichroism and X-ray resonant magnetic reflectometry investigations on the spectroscopic nature of uncompensated pinned magnetic moments in the antiferromagnetic layer of a typical exchange bias system. Unexpectedly, the pinned moments exhibit nearly pure orbital moment character. This strong orbital pinning mechanism has not been observed so far and is not discussed in literature regarding any theory for local magnetocrystalline anisotropy energies in magnetic systems. To verify this new phenomenon we investigated the effect at different temperatures. We provide a simple model discussing the observed pure orbital moments, based on rotatable spin magnetic moments and pinned orbital moments on the same atom. This unexpected observation leads to a concept for a new type of anisotropy energy.
KW  - pinned orbital moments
KW  - ferromagnet
KW  - antiferromagnet
KW  - anisotropy energy
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-167727
VL  - 6
IS  - 25517
ER  - 
TY  - JOUR
A1  - Horikiri, Tomoyuki
A1  - Yamaguchi, Makoto
A1  - Kamide, Kenji
A1  - Matsuo, Yasuhiro
A1  - Byrnes, Tim
A1  - Ishida, Natsuko
A1  - Löffler, Andreas
A1  - Höfling, Sven
A1  - Shikano, Yutaka
A1  - Ogawa, Tetsuo
A1  - Forchel, Alfred
A1  - Yamamoto, Yoshihisa
T1  - High-energy side-peak emission of exciton-polariton condensates in high density regime
JF  - Scientific Reports
N2  - In a standard semiconductor laser, electrons and holes recombine via stimulated emission to emit coherent light, in a process that is far from thermal equilibrium. Exciton-polariton condensates–sharing the same basic device structure as a semiconductor laser, consisting of quantum wells coupled to a microcavity–have been investigated primarily at densities far below the Mott density for signatures of Bose-Einstein condensation. At high densities approaching the Mott density, exciton-polariton condensates are generally thought to revert to a standard semiconductor laser, with the loss of strong coupling. Here, we report the observation of a photoluminescence sideband at high densities that cannot be accounted for by conventional semiconductor lasing. This also differs from an upper-polariton peak by the observation of the excitation power dependence in the peak-energy separation. Our interpretation as a persistent coherent electron-hole-photon coupling captures several features of this sideband, although a complete understanding of the experimental data is lacking. A full understanding of the observations should lead to a development in non-equilibrium many-body physics.
KW  - side-peak emission
KW  - exciton-polariton condensates
KW  - standard semiconductor laser
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-167711
VL  - 6
IS  - 25655
ER  - 
TY  - JOUR
A1  - Estrecho, E.
A1  - Gao, T.
A1  - Brodbeck, S.
A1  - Kamp, M.
A1  - Schneider, C.
A1  - Höfling, S.
A1  - Truscott, A. G.
A1  - Ostrovskaya, E. A.
T1  - Visualising Berry phase and diabolical points in a quantum exciton-polariton billiard
JF  - Scientific Reports
N2  - Diabolical points (spectral degeneracies) can naturally occur in spectra of two-dimensional quantum systems and classical wave resonators due to simple symmetries. Geometric Berry phase is associated with these spectral degeneracies. Here, we demonstrate a diabolical point and the corresponding Berry phase in the spectrum of hybrid light-matter quasiparticles—exciton-polaritons in semiconductor microcavities. It is well known that sufficiently strong optical pumping can drive exciton-polaritons to quantum degeneracy, whereby they form a macroscopically populated quantum coherent state similar to a Bose-Einstein condensate. By pumping a microcavity with a spatially structured light beam, we create a two-dimensional quantum billiard for the exciton-polariton condensate and demonstrate a diabolical point in the spectrum of the billiard eigenstates. The fully reconfigurable geometry of the potential walls controlled by the optical pump enables a striking experimental visualization of the Berry phase associated with the diabolical point. The Berry phase is observed and measured by direct imaging of the macroscopic exciton-polariton probability densities.
KW  - Berry phase
KW  - diabolical points
KW  - quantum billiard
KW  - exciton-polariton
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-167496
VL  - 6
IS  - 37653
ER  - 
TY  - JOUR
A1  - Kim, Seonghoon
A1  - Zhang, Bo
A1  - Wang, Zhaorong
A1  - Fischer, Julian
A1  - Brodbeck, Sebastian
A1  - Kamp, Martin
A1  - Schneider, Christian
A1  - Höfling, Sven
A1  - Deng, Hui
T1  - Coherent Polariton Laser
JF  - Physical Review X
N2  - The semiconductor polariton laser promises a new source of coherent light, which, compared to conventional semiconductor photon lasers, has input-energy threshold orders of magnitude lower. However, intensity stability, a defining feature of a coherent state, has remained poor. Intensity noise many times the shot noise of a coherent state has persisted, attributed to multiple mechanisms that are difficult to separate in conventional polariton systems. The large intensity noise, in turn, limits the phase coherence. Thus, the capability of the polariton laser as a source of coherence light is limited. Here, we demonstrate a polariton laser with shot-noise-limited intensity stability, as expected from a fully coherent state. This stability is achieved by using an optical cavity with high mode selectivity to enforce single-mode lasing, suppress condensate depletion, and establish gain saturation. Moreover, the absence of spurious intensity fluctuations enables the measurement of a transition from exponential to Gaussian decay of the phase coherence of the polariton laser. It suggests large self-interaction energies in the polariton condensate, exceeding the laser bandwidth. Such strong interactions are unique to matter-wave lasers and important for nonlinear polariton devices. The results will guide future development of polariton lasers and nonlinear polariton devices.
KW  - polariton laser
KW  - condensed matter physics
KW  - photonics
KW  - quantum physics
KW  - coherent light
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-166597
VL  - 6
IS  - 011026
ER  - 
TY  - JOUR
A1  - Redlich, Christoph
A1  - Lingnau, Benjamin
A1  - Holzinger, Steffen
A1  - Schlottmann, Elisabeth
A1  - Kreinberg, Sören
A1  - Schneider, Christian
A1  - Kamp, Martin
A1  - Höfling, Sven
A1  - Wolters, Janik
A1  - Reitzenstein, Stephan
A1  - Lüdge, Kathy
T1  - Mode-switching induced super-thermal bunching in quantum-dot microlasers
JF  - New Journal of Physics
N2  - The super-thermal photon bunching in quantum-dot (QD) micropillar lasers is investigated both experimentally and theoretically via simulations driven by dynamic considerations. Using stochastic multi-mode rate equations we obtain very good agreement between experiment and theory in terms of intensity profiles and intensity-correlation properties of the examined QD micro-laser's emission. Further investigations of the time-dependent emission show that super-thermal photon bunching occurs due to irregular mode-switching events in the bimodal lasers. Our bifurcation analysis reveals that these switchings find their origin in an underlying bistability, such that spontaneous emission noise is able to effectively perturb the two competing modes in a small parameter region. We thus ascribe the observed high photon correlation to dynamical multistabilities rather than quantum mechanical correlations.
KW  - microlaser
KW  - nonlinear dynamics
KW  - correlation properties
KW  - photon statistics
KW  - noise and multimode dynamics
KW  - quantum dot laser
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-166286
VL  - 18
IS  - 063011
ER  - 
TY  - JOUR
A1  - Hargart, F
A1  - Roy-Choudhury, K
A1  - John, T
A1  - Portalupi, S L
A1  - Schneider, C
A1  - Höfling, S
A1  - Kamp, M
A1  - Hughes, S
A1  - Michler, P
T1  - Probing different regimes of strong field light-matter interaction with semiconductor quantum dots and few cavity photons
JF  - New Journal of Physics
N2  - In this work we present an extensive experimental and theoretical investigation of different regimes of strong field light–matter interaction for cavity-driven quantum dot (QD) cavity systems. The electric field enhancement inside a high-Q micropillar cavity facilitates exceptionally strong interaction with few cavity photons, enabling the simultaneous investigation for a wide range of QD-laser detuning. In case of a resonant drive, the formation of dressed states and a Mollow triplet sideband splitting of up to 45 μeV is measured for amean cavity photon number <n\(_c\)>\(\leq\) 1. In the asymptotic limit of the linear ACStark effect we systematically investigate the power and detuning dependence of more than 400 QDs. Some QD-cavity systems exhibit an unexpected anomalous Stark shift, which can be explained by an extended dressed 4-levelQDmodel.Weprovide a detailed analysis of the QD-cavity systems properties enabling this novel effect. The experimental results are successfully reproduced using a polaron master equation approach for the QD-cavity system, which includes the driving laser field, exciton-cavity and exciton-phonon interactions
KW  - light–matter interaction
KW  - quantum dots
KW  - AC Stark effect
KW  - dressed states
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-166278
VL  - 18
ER  - 
TY  - JOUR
A1  - Jahnke, Frank
A1  - Gies, Christopher
A1  - Aßmann, Marc
A1  - Bayer, Manfred
A1  - Leymann, H.A.M.
A1  - Foerster, Alexander
A1  - Wiersig, Jan
A1  - Schneider, Christian
A1  - Kamp, Martin
A1  - Höfling, Sven
T1  - Giant photon bunching, superradiant pulse emission and excitation trapping in quantum-dot nanolasers
JF  - Nature Communications
N2  - Light is often characterized only by its classical properties, like intensity or coherence. When looking at its quantum properties, described by photon correlations, new information about the state of the matter generating the radiation can be revealed. In particular the difference between independent and entangled emitters, which is at the heart of quantum mechanics, can be made visible in the photon statistics of the emitted light. The well-studied phenomenon of superradiance occurs when quantum–mechanical correlations between the emitters are present. Notwithstanding, superradiance was previously demonstrated only in terms of classical light properties. Here, we provide the missing link between quantum correlations of the active material and photon correlations in the emitted radiation. We use the superradiance of quantum dots in a cavity-quantum electrodynamics laser to show a direct connection between superradiant pulse emission and distinctive changes in the photon correlation function. This directly demonstrates the importance of quantum–mechanical correlations and their transfer between carriers and photons in novel optoelectronic devices.
KW  - photon bunching
KW  - quantum mechanics
KW  - superradiant pulse emission
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-166144
VL  - 7
IS  - 11540
ER  - 
TY  - JOUR
A1  - Yilmaz, Ali
A1  - Rösch, Sabine
A1  - Klingel, Karin
A1  - Kandolf, Reinhard
A1  - Helluy, Xavier
A1  - Hiller, Karl-Heinz
A1  - Jakob, Peter M
A1  - Sechtem, Udo
T1  - Molecular magnetic resonance imaging (MRI) of inflamed myocardium using ferucarbotran in patients with acute myocardial infarction
JF  - Journal of Cardiovascular Magnetic Resonance
N2  - Introduction:
Superparamagnetic iron oxide nanoparticle (SPIO)-based
molecular imaging agents targeting macrophages have
been developed and successfully applied in animal models
of myocardial infarction.
KW  - Acute Myocardial Infarction
KW  - Cardiovascular Magnetic Resonance
KW  - Iron Oxide Nanoparticle
KW  - Superparamagnetic Iron Oxide
KW  - Infarct Zone
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-140991
VL  - 13
IS  - Suppl. 1
ER  - 
TY  - JOUR
T1  - Measurement of the inelastic proton–proton cross-section at √s=7 TeV with the ATLAS detector
JF  - Nature Communications
N2  - The dependence of the rate of proton–proton interactions on the centre-of-mass collision energy, √s, is of fundamental importance for both hadron collider physics and particle astrophysics. The dependence cannot yet be calculated from first principles; therefore, experimental measurements are needed. Here we present the first measurement of the inelastic proton–proton interaction cross-section at a centre-of-mass energy, √s, of 7 TeV using the ATLAS detector at the Large Hadron Collider. Events are selected by requiring hits on scintillation counters mounted in the forward region of the detector. An inelastic cross-section of 60.3±2.1 mb is measured for ξ>5×10−6, where ξ is calculated from the invariant mass, MX, of hadrons selected using the largest rapidity gap in the event. For diffractive events, this corresponds to requiring at least one of the dissociation masses to be larger than 15.7 GeV.
KW  - Physical Sciences
KW  - Particle physics
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-140960
VL  - 2
ER  - 
TY  - JOUR
A1  - Razinskas, Gary
A1  - Biagioni, Paolo
A1  - Hecht, Bert
T1  - Limits of Kirchhoff’s laws in plasmonics
JF  - Scientific Reports
N2  - The validity of Kirchhoff’s laws in plasmonic nanocircuitry is investigated by studying a junction of plasmonic two-wire transmission lines. We find that Kirchhoff’s laws are valid for sufficiently small values of a phenomenological parameter κ relating the geometrical parameters of the transmission line with the effective wavelength of the guided mode. Beyond such regime, for large values of the phenomenological parameter, increasing deviations occur and the equivalent impedance description (Kirchhoff’s laws) can only provide rough, but nevertheless useful, guidelines for the design of more complex plasmonic circuitry. As an example we investigate a system composed of a two-wire transmission line and a nanoantenna as the load. By addition of a parallel stub designed according to Kirchhoff’s laws we achieve maximum signal transfer to the nanoantenna.
KW  - integrated optics
KW  - nanowires
KW  - plasmonics
KW  - Kirchhoff's law
Y1  - 2018
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-176080
VL  - 8
IS  - 1921
ER  - 
TY  - JOUR
A1  - Han, Luyang
A1  - Wiedwald, Ulf
A1  - Biskupek, Johannes
A1  - Fauth, Kai
A1  - Kaiser, Ute
A1  - Ziemann, Paul
T1  - Nanoscaled alloy formation from self-assembled elemental Co nanoparticles on top of Pt films
JF  - Beilstein Journal of Nanotechnology
N2  - The thermally activated formation of nanoscale CoPt alloys was investigated, after deposition of self-assembled Co nanoparticles on textured Pt(111) and epitaxial Pt(100) films on MgO(100) and SrTiO3(100) substrates, respectively. For this purpose, metallic Co nanoparticles (diameter 7 nm) were prepared with a spacing of 100 nm by deposition of precursor-loaded reverse micelles, subsequent plasma etching and reduction on flat Pt surfaces. The samples were then annealed at successively higher temperatures under a H2 atmosphere, and the resulting variations of their structure, morphology and magnetic properties were characterized. We observed pronounced differences in the diffusion and alloying of Co nanoparticles on Pt films with different orientations and microstructures. On textured Pt(111) films exhibiting grain sizes (20–30 nm) smaller than the particle spacing (100 nm), the formation of local nanoalloys at the surface is strongly suppressed and Co incorporation into the film via grain boundaries is favoured. In contrast, due to the absence of grain boundaries on high quality epitaxial Pt(100) films with micron-sized grains, local alloying at the film surface was established. Signatures of alloy formation were evident from magnetic investigations. Upon annealing to temperatures up to 380 °C, we found an increase both of the coercive field and of the Co orbital magnetic moment, indicating the formation of a CoPt phase with strongly increased magnetic anisotropy compared to pure Co. At higher temperatures, however, the Co atoms diffuse into a nearby surface region where Pt-rich compounds are formed, as shown by element-specific microscopy.
KW  - alloy
KW  - CoPt
KW  - HRTEM
KW  - nanoparticles
KW  - XMCD
KW  - Co
KW  - epitaxy
KW  - magnetometry
KW  - Pt
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-142869
VL  - 2
ER  - 
TY  - JOUR
A1  - Hertlein, Tobias
A1  - Sturm, Volker
A1  - Kircher, Stefan
A1  - Basse-Lüsebrink, Thomas
A1  - Haddad, Daniel
A1  - Ohlsen, Knut
A1  - Jakob, Peter
T1  - Visualization of Abscess Formation in a Murine Thigh Infection Model of \(Staphylococcus\) \(aureus\) by (19)F-Magnetic Resonance Imaging (MRI)
JF  - PLoS ONE
N2  - Background: 

During the last years, (19)F-MRI and perfluorocarbon nanoemulsion (PFC) emerged as a powerful contrast agent methodology to track cells and to visualize inflammation. We applied this new modality to visualize deep tissue abscesses during acute and chronic phase of inflammation caused by Staphylococcus aureus infection. 

Methodology and Principal Findings: 

In this study, a murine thigh infection model was used to induce abscess formation and PFC or CLIO (cross linked ironoxides) was administered during acute or chronic phase of inflammation. 24 h after inoculation, the contrast agent accumulation was imaged at the site of infection by MRI. Measurements revealed a strong accumulation of PFC at the abscess rim at acute and chronic phase of infection. The pattern was similar to CLIO accumulation at chronic phase and formed a hollow sphere around the edema area. Histology revealed strong influx of neutrophils at the site of infection and to a smaller extend macrophages during acute phase and strong influx of macrophages at chronic phase of inflammation. 

Conclusion and Significance: 

We introduce (19)F-MRI in combination with PFC nanoemulsions as a new platform to visualize abscess formation in a murine thigh infection model of S. aureus. The possibility to track immune cells in vivo by this modality offers new opportunities to investigate host immune response, the efficacy of antibacterial therapies and the influence of virulence factors for pathogenesis.
KW  - Soft-tissue infection
KW  - In-vivo
KW  - Iron-oxide
KW  - F-19 MRI
KW  - Inflammation
KW  - Particles
KW  - Tracking
KW  - Lesions
KW  - Images
KW  - Rats
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-142846
VL  - 6
IS  - 3
ER  - 
TY  - JOUR
T1  - Two-particle Bose-Einstein correlations in pp collisions at \(\sqrt {s}\) = 0.9 and 7 TeV measured with the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - The paper presents studies of Bose–Einstein Correlations (BEC) for pairs of like-sign charged particles measured in the kinematic range p\(_{T}\) > 100 MeV and |η| <  2.5 in proton collisions at centre-of-mass energies of 0.9 and 7 TeV with the ATLAS detector at the CERN Large Hadron Collider. The integrated luminosities are approximately 7 μb\(^{−1}\), 190 μb\(^{−1}\) and 12.4 nb\(^{−1}\) for 0.9 TeV, 7 TeV minimum-bias and 7 TeV high-multiplicity data samples, respectively. The multiplicity dependence of the BEC parameters characterizing the correlation strength and the correlation source size are investigated for charged-particle multiplicities of up to 240. A saturation effect in the multiplicity dependence of the correlation source size parameter is observed using the high-multiplicity 7 TeV data sample. The dependence of the BEC parameters on the average transverse momentum of the particle pair is also investigated.
KW  - ATLAS detector
KW  - proton-proton collision
KW  - Bose-Einstein Correlations
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150222
VL  - 75
IS  - 10
ER  - 
TY  - JOUR
T1  - Search for the Standard Model Higgs boson produced in association with top quarks and decaying into b\(\overline{b}\) in pp collisions at \(\sqrt {s}\) = 8 TeV with the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - A search for the Standard Model Higgs boson produced in association with a top-quark pair, t\(\overline{t}\)H, is presented. The analysis uses 20.3 fb\(^{−1}\) of pp collision data at \(\sqrt {s}\) = 8 TeV, collected with the ATLAS detector at the Large Hadron Collider during 2012. The search is designed for the H→b\(\overline{b}\) decay mode and uses events containing one or two electrons or muons. In order to improve the sensitivity of the search, events are categorised according to their jet and b-tagged jet multiplicities. A neural network is used to discriminate between signal and background events, the latter being dominated by t\(\overline{t}\)+jets production. In the single-lepton channel, variables calculated using a matrix element method are included as inputs to the neural network to improve discrimination of the irreducible t\(\overline{t}\)+b\(\overline{b}\) background. No significant excess of events above the background expectation is found and an observed (expected) limit of 3.4 (2.2) times the Standard Model cross section is obtained at 95 % confidence level. The ratio of the measured t\(\overline{t}\)H signal cross section to the Standard Model expectation is found to be μ = 1.5 ± 1.1 assuming a Higgs boson mass of 125 GeV.
KW  - Higgs boson
KW  - ATLAS detector
KW  - top quarks
KW  - proton-proton collision
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150197
VL  - 75
IS  - 7
ER  - 
TY  - JOUR
T1  - Search for supersymmetry in events containing a same-flavour opposite-sign dilepton pair, jets, and large missing transverse momentum in \(\sqrt {s}\) = 8 TeV pp collisions with the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - Two searches for supersymmetric particles in final states containing a same-flavour opposite-sign lepton pair, jets and large missing transverse momentum are presented. The proton–proton collision data used in these searches were collected at a centre-of-mass energy \(\sqrt {s}\) = 8 TeV by the ATLAS detector at the Large Hadron Collider and corresponds to an integrated luminosity of 20.3 fb\(^{−1}\). Two leptonic production mechanisms are considered: decays of squarks and gluinos with Z bosons in the final state, resulting in a peak in the dilepton invariant mass distribution around the Z-boson mass; and decays of neutralinos (e.g. \(\tilde{χ}\)\(^{0}_{2}\) → ℓ\(^{+}\)ℓ\(^{−}\)\(\tilde{χ}\)\(^{0}_{1}\)), resulting in a kinematic endpoint in the dilepton invariant mass distribution. For the former, an excess of events above the expected Standard Model background is observed, with a significance of three standard deviations. In the latter case, the data are well-described by the expected Standard Model background. The results from each channel are interpreted in the context of several supersymmetric models involving the production of squarks and gluinos.
KW  - ATLAS detector
KW  - supersymmetry
KW  - proton-proton collision
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150184
VL  - 75
IS  - 7
ER  - 
TY  - JOUR
T1  - Search for resonant diboson production in the ℓℓq\(\overline{q}\) final state in pp collisions at \(\sqrt {s}\) = 8 TeV with the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - This paper reports on a search for narrow resonances in diboson production in the ℓℓq\(\overline{q}\) final state using pp collision data corresponding to an integrated luminosity of 20 fb\(^{−1}\) collected at \(\sqrt {s}\) = 8 TeV with the ATLAS detector at the Large Hadron Collider. No significant excess of data events over the Standard Model expectation is observed. Upper limits at the 95 % confidence level are set on the production cross section times branching ratio for Kaluza–Klein gravitons predicted by the Randall–Sundrum model and for Extended Gauge Model W′ bosons. These results lead to the exclusion of mass values below 740 and 1590 GeV for the graviton and W′ boson respectively.
KW  - ATLAS detector
KW  - proton-proton collision
KW  - diboson production
KW  - resonances
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150171
VL  - 75
IS  - 2
ER  - 
TY  - JOUR
T1  - Search for production of WW/WZ resonances decaying to a lepton, neutrino and jets in pp collisions at \(\sqrt {s}\)= 8 TeV with the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - A search is presented for narrow diboson resonances decaying to WW or WZ in the final state where one W boson decays leptonically (to an electron or a muon plus a neutrino) and the other W/Z boson decays hadronically. The analysis is performed using an integrated luminosity of 20.3 fb\(^{−1}\) of pp collisions at \(\sqrt {s}\) = 8 TeV collected by the ATLAS detector at the large hadron collider. No evidence for resonant diboson production is observed, and resonance masses below 700 and 1490 GeV are excluded at 95 % confidence level for the spin-2 Randall–Sundrum bulk graviton G\(^{*}\) with coupling constant of 1.0 and the extended gauge model W′ boson respectively.
KW  - ATLAS detector
KW  - W boson
KW  - Z boson
KW  - proton-proton collision
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150164
VL  - 75
IS  - 5
ER  - 
TY  - JOUR
T1  - Search for new phenomena in final states with an energetic jet and large missing transverse momentum in pp collisions at \(\sqrt {s}\) = 8 TeV with the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - Results of a search for new phenomena in final states with an energetic jet and large missing transverse momentum are reported. The search uses 20.3 fb\(^{−1}\) of \(\sqrt {s}\) = 8 TeV data collected in 2012 with the ATLAS detector at the LHC. Events are required to have at least one jet with pT > 120 GeV and no leptons. Nine signal regions are considered with increasing missing transverse momentum requirements between E\(^{miss}_{T}\) > 150 GeV and E\(^{miss}_{T}\) > 700 GeV. Good agreement is observed between the number of events in data and Standard Model expectations. The results are translated into exclusion limits on models with either large extra spatial dimensions, pair production of weakly interacting dark matter candidates, or production of very light gravitinos in a gauge-mediated supersymmetric model. In addition, limits on the production of an invisibly decaying Higgs-like boson leading to similar topologies in the final state are presented.
KW  - ATLAS detector
KW  - energetic jet
KW  - proton-proton collision
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150152
VL  - 75
IS  - 7
ER  - 
TY  - JOUR
T1  - Search for metastable heavy charged particles with large ionisation energy loss in pp collisions at \(\sqrt {s}\) = 8 TeV using the ATLAS experiment
JF  - European Physical Journal C: Particles and Fields
N2  - Many extensions of the Standard Model predict the existence of charged heavy long-lived particles, such as R-hadrons or charginos. These particles, if produced at the Large Hadron Collider, should be moving non-relativistically and are therefore identifiable through the measurement of an anomalously large specific energy loss in the ATLAS pixel detector. Measuring heavy long-lived particles through their track parameters in the vicinity of the interaction vertex provides sensitivity to metastable particles with lifetimes from 0.6 ns to 30 ns. A search for such particles with the ATLAS detector at the Large Hadron Collider is presented, based on a data sample corresponding to an integrated luminosity of 18.4 fb\(^{−1}\) of pp collisions at \(\sqrt {s}\) = 8 TeV. No significant deviation from the Standard Model background expectation is observed, and lifetime-dependent upper limits on R-hadrons and chargino production are set. Gluino R-hadrons with 10 ns lifetime and masses up to 1185 GeV are excluded at 95 % confidence level, and so are charginos with 15 ns lifetime and masses up to 482 GeV.
KW  - ATLAS detector
KW  - charged heavy long-lived particles
KW  - proton-proton collision
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150149
VL  - 75
IS  - 9
ER  - 
TY  - JOUR
T1  - Search for invisible particles produced in association with single-top-quarks in proton-proton collisions at \(\sqrt {s}\) = 8 TeV with the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - A search for the production of single-top-quarks in association with missing energy is performed in proton–proton collisions at a centre-of-mass energy of \(\sqrt {s}\) =8 TeV with the ATLAS experiment at the large hadron collider using data collected in 2012, corresponding to an integrated luminosity of 20.3 fb\(^{−1}\). In this search, the W boson from the top quark is required to decay into an electron or a muon and a neutrino. No deviation from the standard model prediction is observed, and upper limits are set on the production cross-section for resonant and non-resonant production of an invisible exotic state in association with a right-handed top quark. In the case of resonant production, for a spin-0 resonance with a mass of 500 GeV, an effective coupling strength above 0.15 is excluded at 95 % confidence level for the top quark and an invisible spin-1/2 state with mass between 0 and 100 GeV. In the case of non-resonant production, an effective coupling strength above 0.2 is excluded at 95 % confidence level for the top quark and an invisible spin-1 state with mass between 0 and 657 GeV.
KW  - single-top-quarks
KW  - proton-proton collision
KW  - ATLAS detector
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150134
VL  - 75
IS  - 2
ER  - 
TY  - JOUR
T1  - Search for invisible decays of the Higgs boson produced in association with a hadronically decaying vector boson in pp collisions at \(\sqrt {s}\) = TeV with the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - A search for Higgs boson decays to invisible particles is performed using 20.3 fb\(^{−1}\) of pp collision data at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector at the Large Hadron Collider. The process considered is Higgs boson production in association with a vector boson (V = W or Z) that decays hadronically, resulting in events with two or more jets and large missing transverse momentum. No excess of candidates is observed in the data over the background expectation. The results are used to constrain VH production followed by H decaying to invisible particles for the Higgs boson mass range 115 < m\(_{H}\) < 300 GeV. The 95 % confidence-level observed upper limit on σ\(_{VH}\) × BR(H → inv.) varies from 1.6 pb at 115 GeV to 0.13 pb at 300 GeV. Assuming Standard Model production and including the gg → H contribution as signal, the results also lead to an observed upper limit of 78 % at 95 % confidence level on the branching ratio of Higgs bosons decays to invisible particles at a mass of 125 GeV.
KW  - Higgs boson
KW  - ATLAS detector
KW  - decays
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150126
VL  - 75
IS  - 7
ER  - 
TY  - JOUR
T1  - Search for Higgs boson pair production in the b\(\overline{b}\)b\(\overline{b}\) final state from pp collisions at \(\sqrt {s}\) = 8 TeV with the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - A search for Higgs boson pair production pp → hh is performed with 19.5 fb\(^{−1}\) of proton–proton collision data at \(\sqrt {s}\) = 8 TeV, which were recorded by the ATLAS detector at the Large Hadron Collider in 2012. The decay products of each Higgs boson are reconstructed as a high-momentum b\(\overline{b}\) system with either a pair of small-radius jets or a single large-radius jet, the latter exploiting jet substructure techniques and associated b-tagged track-jets. No evidence for resonant or non-resonant Higgs boson pair production is observed. The data are interpreted in the context of the Randall–Sundrum model with a warped extra dimension as well as the two-Higgs-doublet model. An upper limit on the cross-section for pp → G\(^{*}_{KK}\) → hh → b\(\overline{b}\)b\(\overline{b}\) of 3.2(2.3) fb is set for a Kaluza–Klein graviton G\(^{*}_{KK}\) mass of 1.0(1.5) TeV, at the 95 % confidence level. The search for non-resonant Standard Model hh production sets an observed 95 % confidence level upper limit on the production cross-section σ(pp → hh → b\(\overline{b}\)b\(\overline{b}\)) of 202 fb, compared to a Standard Model prediction of σ(pp → hh → b\(\overline{b}\)b\(\overline{b}\)) = 3.6±0.5 fb.
KW  - Higgs boson
KW  - proton-proton collision
KW  - ATLAS detector
KW  - pair production
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150119
VL  - 75
IS  - 9
ER  - 
TY  - JOUR
T1  - Search for heavy long-lived multi-charged particles in pp collisions at \(\sqrt {s}\) = 8 TeV using the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - A search for heavy long-lived multi-charged particles is performed using the ATLAS detector at the LHC. Data collected in 2012 at \(\sqrt {s}\) = 8 TeV from pp collisions corresponding to an integrated luminosity of 20.3 fb\(^{−1}\) are examined. Particles producing anomalously high ionisation, consistent with long-lived massive particles with electric charges from |q| = 2e to |q| = 6e are searched for. No signal candidate events are observed, and 95 % confidence level cross-section upper limits are interpreted as lower mass limits for a Drell–Yan production model. The mass limits range between 660 and 785 GeV.
KW  - ATLAS detector
KW  - proton-proton collision
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150100
VL  - 75
IS  - 8
ER  - 
TY  - JOUR
T1  - Search for direct pair production of a chargino and a neutralino decaying to the 125 GeV Higgs boson in \(\sqrt {s}\) = 8 TeV pp collisions with the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - A search is presented for the direct pair production of a chargino and a neutralino pp → \(\tilde{χ}\)\(^{±}_{1}\)\(\tilde{χ}\)\(^{0}_{2}\), where the chargino decays to the lightest neutralino and the W boson, \(\tilde{χ}\)\(^{±}_{1}\)→\(\tilde{χ}\)\(^{0}_{1}\)(W\(^{±}\)→ℓ\(^{±}\)ν), while the neutralino decays to the lightest neutralino and the 125 GeV Higgs boson, \(\tilde{χ}\)\(^{0}_{2}\)→\(\tilde{χ}\)\(^{0}_{1}\)(h→bb/γγ/ℓ\(^{±}\)νqq). The final states considered for the search have large missing transverse momentum, an isolated electron or muon, and one of the following: either two jets identified as originating from bottom quarks, or two photons, or a second electron or muon with the same electric charge. The analysis is based on 20.3 fb\(^{-1}\) of \(\sqrt {s}\) = 8 TeV proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with the Standard Model expectations, and limits are set in the context of a simplified supersymmetric model.
KW  - neutralino
KW  - chargino
KW  - proton-proton collision
KW  - Higgs boson
KW  - ATLAS detector
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150099
VL  - 75
IS  - 5
ER  - 
TY  - JOUR
T1  - Search for dark matter in events with heavy quarks and missing transverse momentum in pp collisions with the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - This article reports on a search for dark matter pair production in association with bottom or top quarks in 20.3 fb\(^{−1}\) of pp collisions collected at \(\sqrt {s}\) = 8 TeV by the ATLAS detector at the LHC. Events with large missing transverse momentum are selected when produced in association with high-momentum jets of which one or more are identified as jets containing b-quarks. Final states with top quarks are selected by requiring a high jet multiplicity and in some cases a single lepton. The data are found to be consistent with the Standard Model expectations and limits are set on the mass scale of effective field theories that describe scalar and tensor interactions between dark matter and Standard Model particles. Limits on the dark-matter–nucleon cross-section for spin-independent and spin-dependent interactions are also provided. These limits are particularly strong for low-mass dark matter. Using a simplified model, constraints are set on the mass of dark matter and of a coloured mediator suitable to explain a possible signal of annihilating dark matter.
KW  - dark matter
KW  - proton-proton collision
KW  - ATLAS detector
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150089
VL  - 75
IS  - 2
ER  - 
TY  - JOUR
T1  - Search for a new resonance decaying to a W or Z boson and a Higgs boson in the ℓℓ/ℓν/νν+b\(\overline{b}\) final states with the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - A search for a new resonance decaying to a W or Z boson and a Higgs boson in the ℓℓ/ℓν/νν+b\(\overline{b}\) final states is performed using 20.3 fb\(^{−1}\) of pp collision data recorded at \(\sqrt {s}\) = 8 TeV with the ATLAS detector at the Large Hadron Collider. The search is conducted by examining the WH / ZH invariant mass distribution for a localized excess. No significant deviation from the Standard Model background prediction is observed. The results are interpreted in terms of constraints on the Minimal Walking Technicolor model and on a simplified approach based on a phenomenological Lagrangian of Heavy Vector Triplets.
KW  - Higgs boson
KW  - W boson
KW  - Z boson
KW  - ATLAS detector
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150075
VL  - 75
IS  - 6
ER  - 
TY  - JOUR
T1  - Search for W' → tb → qqbb decays in pp collisions at \(\sqrt {s}\) = 8 TeV with the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - A search for a massive W′ gauge boson decaying to a top quark and a bottom quark is performed with the ATLAS detector in pp collisions at the LHC. The dataset was taken at a centre-of-mass energy of \(\sqrt {s}\) = 8 TeV and corresponds to 20.3 fb\(^{−1}\) of integrated luminosity. This analysis is done in the hadronic decay mode of the top quark, where novel jet substructure techniques are used to identify jets from high-momentum top quarks. This allows for a search for high-mass W′ bosons in the range 1.5–3.0  TeV. b-tagging is used to identify jets originating from b-quarks. The data are consistent with Standard Model background-only expectations, and upper limits at 95 % confidence level are set on the W′ → tb cross section times branching ratio ranging from 0.16 pb to 0.33 pb for left-handed W′ bosons, and ranging from 0.10 pb to 0.21 pb for W′ bosons with purely right-handed couplings. Upper limits at 95 % confidence level are set on the W′-boson coupling to tb as a function of the W′ mass using an effective field theory approach, which is independent of details of particular models predicting a W′ boson.
KW  - ATLAS detector
KW  - proton-proton collision
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150068
VL  - 75
IS  - 4
ER  - 
TY  - JOUR
T1  - Performance of the ATLAS muon trigger in pp collisions at \(\sqrt {s}\)= 8 TeV
JF  - European Physical Journal C: Particles and Fields
N2  - The performance of the ATLAS muon trigger system is evaluated with proton–proton collision data collected in 2012 at the Large Hadron Collider at a centre-of-mass energy of 8 TeV. It is primarily evaluated using events containing a pair of muons from the decay of Z bosons. The efficiency of the single-muon trigger is measured for muons with transverse momentum 25 < p\(_{T}\) < 100GeV, with a statistical uncertainty of less than 0.01 % and a systematic uncertainty of 0.6 %. The pT range for efficiency determination is extended by using muons from decays of J/ψ mesons, W bosons, and top quarks. The muon trigger shows highly uniform and stable performance. The performance is compared to the prediction of a detailed simulation.
KW  - LHC
KW  - proton-proton-collistion
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-150032
VL  - 75
IS  - 3
ER  - 
TY  - JOUR
T1  - Observation and measurements of the production of prompt and non-prompt J/ψ mesons in association with a Z boson in pp collisions at \(\sqrt {s}\)=8 TeV with the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - The production of a Z boson in association with a J/ψ meson in proton–proton collisions probes the production mechanisms of quarkonium and heavy flavour in association with vector bosons, and allows studies of multiple parton scattering. Using 20.3fb\(^{−1}\) of data collected with the ATLAS experiment at the LHC in pp collisions at \(\sqrt {s}\) = 8 TeV, the first measurement of associated Z+J/ψ production is presented for both prompt and non-prompt J/ψ production, with both signatures having a significance in excess of 5σ. The inclusive production cross-sections for Z boson production (analysed in μ\(^{+}\)μ\(^{−}\) or e\(^{+}\)e\(^{−}\) decay modes) in association with prompt and non-prompt J/ψ(→μ\(^{+}\)μ\(^{−}\)) are measured relative to the inclusive production rate of Z bosons in the same fiducial volume to be (36.8±6.7±2.5)×10\(^{−7}\) and (65.8±9.2±4.2)×10\(^{−7}\) respectively. Normalised differential production cross-section ratios are also determined as a function of the J/ψ transverse momentum. The fraction of signal events arising from single and double parton scattering is estimated, and a lower limit of 5.3 (3.7)mb at 68 (95)% confidence level is placed on the effective cross-section regulating double parton interactions.
KW  - ATLAS detector
KW  - Z boson
KW  - proton-proton-collision
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149970
VL  - 75
IS  - 5
ER  - 
TY  - JOUR
T1  - Measurements of the W production cross sections in association with jets with the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - This paper presents cross sections for the production of a W boson in association with jets, measured in proton–proton collisions at \(\sqrt {s}\) = 7 TeV with the ATLAS experiment at the large hadron collider. With an integrated luminosity of 4.6 fb\(^{−1}\), this data set allows for an exploration of a large kinematic range, including jet production up to a transverse momentum of 1 TeV and multiplicities up to seven associated jets. The production cross sections for W bosons are measured in both the electron and muon decay channels. Differential cross sections for many observables are also presented including measurements of the jet observables such as the rapidities and the transverse momenta as well as measurements of event observables such as the scalar sums of the transverse momenta of the jets. The measurements are compared to numerous QCD predictions including next-to-leading-order perturbative calculations, resummation calculations and Monte Carlo generators.
KW  - ATLAS detector
KW  - W boson
KW  - proton-prton-collision
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149925
VL  - 75
IS  - 2
ER  - 
TY  - JOUR
T1  - Measurement of three-jet production cross-sections in pp collisions at 7 TeV centre-of-mass energy using the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - Double-differential three-jet production cross-sections are measured in proton–proton collisions at a centre-of-mass energy of \(\sqrt {s}\) = 7 TeV using the ATLAS detector at the large hadron collider. The measurements are presented as a function of the three-jet mass (m\(_{jjj}\)), in bins of the sum of the absolute rapidity separations between the three leading jets (|Y\(^{*}\)|). Invariant masses extending up to 5 TeV are reached for 8 < |Y\(^{*}\)| < 10. These measurements use a sample of data recorded using the ATLAS detector in 2011, which corresponds to an integrated luminosity of 4.51 fb\(^{-1}\). Jets are identified using the anti-k\(_{t}\) algorithm with two different jet radius parameters, R = 0.4 and R = 0.6. The dominant uncertainty in these measurements comes from the jet energy scale. Next-to-leading-order QCD calculations corrected to account for non-perturbative effects are compared to the measurements. Good agreement is found between the data and the theoretical predictions based on most of the available sets of parton distribution functions, over the full kinematic range, covering almost seven orders of magnitude in the measured cross-section values.
KW  - proton-proton-collisions
KW  - ATLAS detector
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149918
VL  - 75
IS  - 5
ER  - 
TY  - JOUR
T1  - Measurement of the top-quark mass in the fully hadronic decay channel from ATLAS data at \(\sqrt {s}\)=7TeV
JF  - European Physical Journal C: Particles and Fields
N2  - The mass of the top quark is measured in a data set corresponding to 4.6  fb\(^{-1}\) of proton–proton collisions with centre-of-mass energy \(\sqrt {s}\)=7 TeV collected by the ATLAS detector at the LHC. Events consistent with hadronic decays of top–antitop quark pairs with at least six jets in the final state are selected. The substantial background from multijet production is modelled with data-driven methods that utilise the number of identified b-quark jets and the transverse momentum of the sixth leading jet, which have minimal correlation. The top-quark mass is obtained from template fits to the ratio of three-jet to dijet mass. The three-jet mass is calculated from the three jets produced in a top-quark decay. Using these three jets the dijet mass is obtained from the two jets produced in the W boson decay. The top-quark mass obtained from this fit is thus less sensitive to the uncertainty in the energy measurement of the jets. A binned likelihood fit yields a top-quark mass of m\(_{t}\)= 175.1 ± 1.4 (stat.) ± 1.2 (syst.) GeV.
KW  - ATLAS
KW  - proton–proton collisions
KW  - top-quark mass
KW  - fully hadronic
KW  - LHC
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149905
VL  - 75
IS  - 4
ER  - 
TY  - JOUR
T1  - Measurement of the top quark mass in the t\(\overline{t}\)→ lepton+jets and t\(\overline{t}\)→ dilepton channels using \(\sqrt {s}\)=7 TeV ATLAS data
JF  - European Physical Journal C: Particles and Fields
N2  - The top quark mass was measured in the channels t\(\overline{t}\) → lepton+jets and t\(\overline{t}\) → dilepton (lepton = e,μ) based on ATLAS data recorded in 2011. The data were taken at the LHC with a proton–proton centre-of-mass energy of \(\sqrt {s}\) = 7 TeV and correspond to an integrated luminosity of 4.6 fb\(^{-1}\). The t\(\overline{t}\) → lepton+jets analysis uses a three-dimensional template technique which determines the top quark mass together with a global jet energy scale factor (JSF), and a relative b-to-light-jet energy scale factor(bJSF), where the terms b-jets and light-jets refer to jets originating from b-quarks and u, d, c, s-quarks or gluons, respectively. The analysis of the t\(\overline{t}\) → dilepton channel exploits a one-dimensional template method using the m\(_{lb}\) observable, defined as the average invariant mass of the two lepton+b-jet pairs in each event. The top quark
mass is measured to be 172.33±0.75(stat + JSF + bJSF)±1.02(syst) GeV, and 173.79 ± 0.54(stat) ± 1.30(syst) GeV in the t\(\overline{t}\) → lepton+jets and t\(\overline{t}\) → dilepton channels, respectively. The combination of the two results yields m\(_{top}\) =172.99 ± 0.48(stat) ± 0.78(syst) GeV, with a total uncertainty of 0.91 GeV.
KW  - top quark mass
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149890
VL  - 75
IS  - 7
ER  - 
TY  - JOUR
T1  - Measurement of the production and lepton charge asymmetry of bosons in Pb+Pb collisions at \(\sqrt {^{S}NN}\) with the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - A measurement of W boson production in lead-lead collisions at \(\sqrt {^{S}NN}\)=2.76 TeV is presented. It is based on the analysis of data collected with the ATLAS detector at the LHC in 2011 corresponding to an integrated luminosity of 0.14 nb\(^{-1}\) and 0.15 nb\(^{-1}\) in the muon and electron decay channels, respectively. The differential production yields and lepton charge asymmetry are each measured as a function of the average number of participating nucleons ⟨N\(_{part}\)⟩ and absolute pseudorapidity of the charged lepton. The results are compared to predictions based on next-to-leading-order QCD calculations. These measurements are, in principle, sensitive to possible nuclear modifications to the parton distribution functions and also provide information on scaling of W boson production in multi-nucleon systems.
KW  - Higgs boson
KW  - lead-lead collision
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149889
VL  - 75
IS  - 1
ER  - 
TY  - JOUR
T1  - Jet energy measurement and its systematic uncertainty in proton-proton collisions at \(\sqrt {s}\)=7  TeV with the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - The jet energy scale (JES) and its systematic uncertainty are determined for jets measured with the ATLAS detector using proton–proton collision data with a centre-of-mass energy of \(\sqrt {s}\)=7 TeV corresponding to an integrated luminosity of 4.7  fb\(^{-1}\). Jets are reconstructed from energy deposits forming topological clusters of calorimeter cells using the anti-k\(_t\) algorithm with distance parameters R=0.4 or R=0.6, and are calibrated using MC simulations. A residual JES correction is applied to account for differences between data and MC simulations. This correction and its systematic uncertainty are estimated using a combination of in situ techniques exploiting the transverse momentum balance between a jet and a reference object such as a photon or a Z boson, for 20≤p\(^{jet}_{T}\)<1000 GeV and pseudorapidities |η|<4.5. The effect of multiple proton–proton interactions is corrected for, and an uncertainty is evaluated using in situ techniques. The smallest JES uncertainty of less than 1 % is found in the central calorimeter region (|η|<1.2) for jets with 55≤p\(^{jet}_{T}\)<500 GeV. For central jets at lower p\(_{T}\), the uncertainty is about 3 %. A consistent JES estimate is found using measurements of the calorimeter response of single hadrons in proton–proton collisions and test-beam data, which also provide the estimate for p\(^{jet}_{T}\)>1 TeV. The calibration of forward jets is derived from dijet p\(_{T}\) balance measurements. The resulting uncertainty reaches its largest value of 6 % for low-p\(_{T}\) jets at |η|=4.5. Additional JES uncertainties due to specific event topologies, such as close-by jets or selections of event samples with an enhanced content of jets originating from light quarks or gluons, are also discussed. The magnitude of these uncertainties depends on the event sample used in a given physics analysis, but typically amounts to 0.5–3 %.
KW  - jet energy scale
KW  - proton-proton-collision
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149854
VL  - 75
IS  - 1
ER  - 
TY  - JOUR
T1  - Identification and energy calibration of hadronically decaying tau leptons with the ATLAS experiment in pp collisions at \(\sqrt {s}\)=8 TeV
JF  - European Physical Journal C: Particles and Fields
N2  - This paper describes the trigger and offline reconstruction, identification and energy calibration algorithms for hadronic decays of tau leptons employed for the data collected from pp collisions in 2012 with the ATLAS detector at the LHC center-of-mass energy \(\sqrt {s}\)=8 TeV. The performance of these algorithms is measured in most cases with Z decays to tau leptons using the full 2012 dataset, corresponding to an integrated luminosity of 20.3 fb\(^{-1}\). An uncertainty on the offline reconstructed tau energy scale of 2–4 %, depending on transverse energy and pseudorapidity, is achieved using two independent methods. The offline tau identification efficiency is measured with a precision of 2.5 % for hadronically decaying tau leptons with one associated track, and of 4 % for the case of three associated tracks, inclusive in pseudorapidity and for a visible transverse energy greater than 20 GeV. For hadronic tau lepton decays selected by offline algorithms, the tau trigger identification efficiency is measured with a precision of 2–8 %, depending on the transverse energy. The performance of the tau algorithms, both offline and at the trigger level, is found to be stable with respect to the number of concurrent proton–proton interactions and has supported a variety of physics results using hadronically decaying tau leptons at ATLAS.
KW  - tau leptons
KW  - hadronic decays
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149829
VL  - 75
IS  - 7
ER  - 
TY  - JOUR
T1  - Determination of spin and parity of the Higgs boson in the WW\(^{*}\)→eνμν decay channel with the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - Studies of the spin and parity quantum numbers of the Higgs boson in the WW\(^{*}\)→eνμν final state are presented, based on proton–proton collision data collected by the ATLAS detector at the Large Hadron Collider, corresponding to an integrated luminosity of 20.3 fb\(^{-1}\) at a centre-of-mass energy of \(\sqrt {s}\)=8 TeV. The Standard Model spin-parity J\(^{CP}\)=0\(^{++}\) hypothesis is compared with alternative hypotheses for both spin and CP. The case where the observed resonance is a mixture of the Standard-Model-like Higgs boson and CP-even (J\(^{CP}\)=0\(^{++}\)) or CP-odd (J\(^{CP}\)=0\(^{+-}\)) Higgs boson in scenarios beyond the Standard Model is also studied. The data are found to be consistent with the Standard Model prediction and limits are placed on alternative spin and CP hypotheses, including CP mixing in different scenarios.
KW  - Higgs boson
KW  - spin
KW  - parity
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149632
VL  - 75
IS  - 5
ER  - 
TY  - JOUR
T1  - Constraints on the off-shell Higgs boson signal strength in the high-mass ZZ and WW final states with the ATLAS detector
JF  - European Physical Journal C: Particles and Fields
N2  - Measurements of the ZZ and WW final states in the mass range above the 2m\(_Z\) and 2m\(_W\) thresholds provide a unique opportunity to measure the off-shell coupling strength of the Higgs boson. This paper presents constraints on the off-shell Higgs boson event yields normalised to the Standard Model prediction (signal strength) in the ZZ→4ℓ, ZZ→2ℓ2ν and WW→eνμν final states. The result is based on pp collision data collected by the ATLAS experiment at the LHC, corresponding to an integrated luminosity of 20.3 fb\(^{-1}\) at a collision energy of \(\sqrt {s}\)=8 TeV. Using the CL\(_S\) method, the observed 95 % confidence level (CL) upper limit on the off-shell signal strength is in the range 5.1–8.6, with an expected range of 6.7–11.0. In each case the range is determined by varying the unknown gg→ZZ and gg→WW background K-factor from higher-order quantum chromodynamics corrections between half and twice the value of the known signal K-factor. Assuming the relevant Higgs boson couplings are independent of the energy scale of the Higgs boson production, a combination with the on-shell measurements yields an observed (expected) 95 % CL upper limit on Γ\(_H\)/Γ\(^{SM}_{H}\) in the range 4.5–7.5 (6.5–11.2) using the same variations of the background K-factor. Assuming that the unknown gg→VV background K-factor is equal to the signal K-factor, this translates into an observed (expected) 95 % CL upper limit on the Higgs boson total width of 22.7 (33.0) MeV.
KW  - Higgs boson
KW  - coupling strength
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149615
VL  - 75
IS  - 7
ER  - 
TY  - JOUR
A1  - Pham, Mirko
A1  - Helluy, Xavier
A1  - Kleinschnitz, Christoph
A1  - Kraft, Peter
A1  - Bartsch, Andreas J.
A1  - Jakob, Peter
A1  - Nieswandt, Bernhard
A1  - Bendszus, Martin
A1  - Guido, Stoll
T1  - Sustained Reperfusion after Blockade of Glycoprotein-Receptor-Ib in Focal Cerebral Ischemia: An MRI Study at 17.6 Tesla
JF  - PLoS ONE
N2  - Background: 

Inhibition of early platelet adhesion by blockade of glycoprotein-IB (GPIb) protects mice from ischemic stroke. To elucidate underlying mechanisms in-vivo, infarct development was followed by ultra-high field MRI at 17.6 Tesla. 

Methods: 

Cerebral infarction was induced by transient-middle-cerebral-artery-occlusion (tMCAO) for 1 hour in C57/BL6 control mice (N = 10) and mice treated with 100 mg Fab-fragments of the GPIb blocking antibody p0p/B 1 h after tMCAO (N = 10). To control for the effect of reperfusion, additional mice underwent permanent occlusion and received anti-GPIb treatment (N = 6; pMCAO) or remained without treatment (N = 3; pMCAO). MRI 2 h and 24 h after MCAO measured cerebral-blood-flow (CBF) by continuous arterial-spin labelling, the apparent-diffusion-coefficient (ADC), quantitative-T2 and T2-weighted imaging. All images were registered to a standard mouse brain MRI atlas and statistically analysed voxel-wise, and by cortico-subcortical ROI analysis. 

Results: 

Anti-GPIb treatment led to a relative increase of postischemic CBF vs. controls in the cortical territory of the MCA (2 h: 44.2 +/- 6.9 ml/100g/min versus 24 h: 60.5 +/- 8.4; p = 0.0012, F((1,18)) = 14.63) after tMCAO. Subcortical CBF 2 h after tMCAO was higher in anti-GPIb treated animals (45.3 +/- 5.9 vs. controls: 33.6 +/- 4.3; p = 0.04). In both regions, CBF findings were clearly related to a lower probability of infarction (Cortex/Subcortex of treated group: 35%/65% vs. controls: 95%/100%) and improved quantitative-T2 and ADC. After pMCAO, anti-GPIb treated mice developed similar infarcts preceded by severe irreversible hypoperfusion as controls after tMCAO indicating dependency of stroke protection on reperfusion. 

Conclusion: 

Blockade of platelet adhesion by anti-GPIb-Fab-fragments results in substantially improved CBF early during reperfusion. This finding was in exact spatial correspondence with the prevention of cerebral infarction and indicates in-vivo an increased patency of the microcirculation. Thus, progression of infarction during early ischemia and reperfusion can be mitigated by anti-platelet treatment.
KW  - Von-Willebrand-factor
KW  - Experimental stroke
KW  - Magnetic-resonance
KW  - Arterial water
KW  - Brain
KW  - Perfusion
KW  - Mice
KW  - Inflammation
KW  - Coefficient
KW  - mechanisms
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-142608
VL  - 6
IS  - 4
ER  - 
TY  - JOUR
T1  - Measurement of exclusive γγ→ℓ\(^{+}\)ℓ\(^{−}\) production in proton–proton collisions at \(\sqrt {s}\)=7 TeV with the ATLAS detector
JF  - Physics Letters B
N2  - This Letter reports a measurement of the exclusive γγ→ℓ\(^{+}\)ℓ\(^{−}\) (ℓ=e, μℓ=e, μ) cross-section in proton–proton collisions at a centre-of-mass energy of 7 TeV by the ATLAS experiment at the LHC, based on an integrated luminosity of 4.6 fb\(^{−1}\). For the electron or muon pairs satisfying exclusive selection criteria, a fit to the dilepton acoplanarity distribution is used to extract the fiducial cross-sections. The cross-section in the electron channel is determined to be \(^{excl.}_{γγ→e^{+}e^{-}}\)=0.428 ± 0.035 (stat.) ± 0.018 (syst.) pb for a phase–space region with invariant mass of the electron pairs greater than 24 GeV, in which both electrons have transverse momentum p\(_{T}\)>12 GeV and pseudorapidity |η|<2.4. For muon pairs with invariant mass greater than 20 GeV, muon transverse momentum p\(_{T}\)>10 GeV and pseudorapidity |η|<2.4, the cross-section is determined to be \(^{excl.}_{γγ→μ^{+}μ^{-}}\) =0.628 ± 0.032 (stat.) ± 0.021 (syst.) pb. When proton absorptive effects due to the finite size of the proton are taken into account in the theory calculation, the measured cross-sections are found to be consistent with the theory prediction.
KW  - physics
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-144247
VL  - 749
ER  - 
TY  - JOUR
T1  - Search for the associated production of the Higgs boson with a top quark pair in multilepton final states with the ATLAS detector
JF  - Physics Letters B
N2  - A search for the associated production of the Higgs boson with a top quark pair is performed in multilepton final states using 20.3 fb\(^{−1}\) of proton–proton collision data recorded by the ATLAS experiment at \(\sqrt {s}\)=8 TeV at the Large Hadron Collider. Five final states, targeting the decays H→WW\(^{*}\), ττ, and ZZ\(^{*}\), are examined for the presence of the Standard Model (SM) Higgs boson: two same-charge light leptons (e or μ) without a hadronically decaying τ lepton; three light leptons; two same-charge light leptons with a hadronically decaying τ lepton; four light leptons; and one light lepton and two hadronically decaying τ leptons. No significant excess of events is observed above the background expectation. The best fit for the t\(\overline{t}\)H production cross section, assuming a Higgs boson mass of 125 GeV, is 2.1\(^{+1.4}_{-1.2}\) times the SM expectation, and the observed (expected) upper limit at the 95% confidence level is 4.7 (2.4) times the SM rate. The p-value for compatibility with the background-only hypothesis is 1.8σ; the expectation in the presence of a Standard Model signal is 0.9σ.
KW  - physics
KW  - associated production
KW  - Higgs boson
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-144231
VL  - 749
ER  - 
TY  - JOUR
T1  - Measurement of colour flow with the jet pull angle in t\(\overline{t}\) events using the ATLAS detector at \(\sqrt {s}\)=8 TeV
JF  - Physics Letters B
N2  - The distribution and orientation of energy inside jets is predicted to be an experimental handle on colour connections between the hard-scatter quarks and gluons initiating the jets. This Letter presents a measurement of the distribution of one such variable, the jet pull angle. The pull angle is measured for jets produced in t\(\overline{t}\) events with one W boson decaying leptonically and the other decaying to jets using 20.3 fb\(^{−1}\) of data recorded with the ATLAS detector at a centre-of-mass energy of \(\sqrt {s}\)=8 TeV at the LHC. The jet pull angle distribution is corrected for detector resolution and acceptance effects and is compared to various models.
KW  - physics
KW  - colour flow
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-144229
VL  - 750
ER  - 
TY  - JOUR
T1  - Measurement of transverse energy–energy correlations in multi-jet events in pp collisions at \(\sqrt {s}\)=7 TeV using the ATLAS detector and determination of the strong coupling constant αs(m\(_{Z}\))
JF  - Physics Letters B
N2  - High transverse momentum jets produced in pp collisions at a centre of mass energy of 7 TeV are used to measure the transverse energy–energy correlation function and its associated azimuthal asymmetry. The data were recorded with the ATLAS detector at the LHC in the year 2011 and correspond to an integrated luminosity of 158 pb\(^{-1}\). The selection criteria demand the average transverse momentum of the two leading jets in an event to be larger than 250 GeV. The data at detector level are well described by Monte Carlo event generators. They are unfolded to the particle level and compared with theoretical calculations at next-to-leading-order accuracy. The agreement between data and theory is good and provides a precision test of perturbative Quantum Chromodynamics at large momentum transfers. From this comparison, the strong coupling constant given at the Z   boson mass is determined to be αs(m\(_{Z}\))=0.1173±0.0010 (exp.) \(^{+0.0065}_{−0.0026}\) (theo.).
KW  - physics
KW  - high transverse momentum jets
KW  - transverse energy–energy correlation function
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-143398
VL  - 750
ER  - 
TY  - JOUR
T1  - Measurement of the branching ratio Γ(Λ\(^0_b\)→ψ(2S)Λ\(^0\))/Γ(Λ\(^0_b\)→J/ψΛ\(^0\)) with the ATLAS detector
JF  - Physics Letters B
N2  - An observation of the View the Λ\(^0_b\)→ψ(2S)Λ\(^0\) decay and a comparison of its branching fraction with that of the Λ\(^0_b\)→J/ψΛ\(^0\) decay has been made with the ATLAS detector in proton–proton collisions at \(\sqrt {s}\)=8 TeV at the LHC using an integrated luminosity of 20.6 fb\(^{-1}\). The J/ψJ/ψ and ψ(2S) mesons are reconstructed in their decays to a muon pair, while the Λ\(^0\)→pπ\(^-\) decay is exploited for the Λ\(^0\) baryon reconstruction. The Λ\(^0_b\) baryons are reconstructed with transverse momentum p\(_T\)>10 GeV pT>10 GeV and pseudorapidity |η|<2.1. The measured branching ratio of the Λ\(^0_b\)→ψ(2S)Λ\(^0\) and Λ\(^0_b\)→J/ψΛ\(^0\) decays is Γ(Λ\(^0_b\)→ψ(2S)Λ\(^0\))/Γ(Λ\(^0_b\)→J/ψΛ\(^0\))=0.501±0.033(stat)±0.019(syst), lower than the expectation from the covariant quark model.
KW  - physics
KW  - proton–proton collisions
KW  - Large Hadron Collider
KW  - decay
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-143375
VL  - 751
ER  - 
TY  - JOUR
A1  - He, Tao
A1  - Stolte, Matthias
A1  - Burschka, Christian
A1  - Hansen, Nis Hauke
A1  - Musiol, Thomas
A1  - Kälblein, Daniel
A1  - Pflaum, Jens
A1  - Tao, Xutang
A1  - Brill, Jochen
A1  - Würthner, Frank
T1  - Single-crystal field-effect transistors of new Cl\(_{2}\)-NDI polymorph processed by sublimation in air
JF  - Nature Communications
N2  - Physical properties of active materials built up from small molecules are dictated by their molecular packing in the solid state. Here we demonstrate for the first time the growth of n-channel single-crystal field-effect transistors and organic thin-film transistors by sublimation of 2,6-dichloro-naphthalene diimide in air. Under these conditions, a new polymorph with two-dimensional brick-wall packing mode (\(\beta\)-phase) is obtained that is distinguished from the previously reported herringbone packing motif obtained from solution (\(\alpha\)-phase). We are able to fabricate single-crystal field-effect transistors with electron mobilities in air of up to 8.6 cm\(^{2}\)V\(^{-1}\)s\(^{-1}\) (\(\alpha\)-phase) and up to 3.5 cm\(^{2}\)V\(^{-1}\)s\(^{-1}\) (\(\beta\)-phase) on n-octadecyltriethoxysilane-modified substrates. On silicon dioxide, thin-film devices based on \(\beta\)-phase can be manufactured in air giving rise to electron mobilities of 0.37 cm\(^{2}\)V\(^{-1}\)s\(^{-1}\). The simple crystal and thin-film growth procedures by sublimation under ambient conditions avoid elaborate substrate modifications and costly vacuum equipment-based fabrication steps.
KW  - thin-film transistors
KW  - carrier transport
KW  - \(\beta\)-phase
KW  - organic semiconductors
KW  - induced phase transition
KW  - charge transport
KW  - materials design
KW  - \(\alpha\)-phase
KW  - mobility
KW  - pentacene
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149255
VL  - 6
IS  - 5954
ER  - 
TY  - JOUR
A1  - Redelbach, Andreas
T1  - Searches for prompt R-parity-violating supersymmetry at the LHC
JF  - Advances in High Energy Physics
N2  - Searches for supersymmetry (SUSY) at the LHC frequently assume the conservation of R-parity in their design, optimization, and interpretation. In the case that R-parity is not conserved, constraints on SUSY particle masses tend to be weakened with respect to R-parity-conserving models. We review the current status of searches for R-parity-violating (RPV) supersymmetry models at the ATLAS and CMS experiments, limited to 8 TeV search results published or submitted for publication as of the end of March 2015. All forms of renormalisable RPV terms leading to prompt signatures have been considered in the set of analyses under review. Discussing results for searches for prompt R-parity-violating SUSY signatures summarizes the main constraints for various RPV models from LHC Run I and also defines the basis for promising signal regions to be optimized for Run II. In addition to identifying highly constrained regions from existing searches, also gaps in the coverage of the parameter space of RPV SUSY are outlined.
KW  - supergauge transformations
KW  - grand unification
KW  - proton-proton collisions
KW  - particle
KW  - breaking
KW  - standard model
KW  - hadron colliders
KW  - √s=8 TeV
KW  - local supersymmetry
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-149149
VL  - 2015
IS  - 982167
ER  - 
TY  - JOUR
A1  - Hill, Philip J.
A1  - Stritzker, Jochen
A1  - Scadeng, Miriam
A1  - Geissinger, Ulrike
A1  - Haddad, Daniel
A1  - Basse-Lüsebrink, Thomas C.
A1  - Gbureck, Uwe
A1  - Jakob, Peter
A1  - Szalay, Aladar A.
T1  - Magnetic Resonance Imaging of Tumors Colonized with Bacterial Ferritin-Expressing \(Escherichia\) \(coli\)
JF  - PLoS ONE
N2  - Background: 

Recent studies have shown that human ferritin can be used as a reporter of gene expression for magnetic resonance imaging (MRI). Bacteria also encode three classes of ferritin-type molecules with iron accumulation properties. 

Methods and Findings: 

Here, we investigated whether these bacterial ferritins can also be used as MRI reporter genes and which of the bacterial ferritins is the most suitable reporter. Bacterial ferritins were overexpressed in probiotic E. coli Nissle 1917. Cultures of these bacteria were analyzed and those generating highest MRI contrast were further investigated in tumor bearing mice. Among members of three classes of bacterial ferritin tested, bacterioferritin showed the most promise as a reporter gene. Although all three proteins accumulated similar amounts of iron when overexpressed individually, bacterioferritin showed the highest contrast change. By site-directed mutagenesis we also show that the heme iron, a unique part of the bacterioferritin molecule, is not critical for MRI contrast change. Tumor-specific induction of bacterioferritin-expression in colonized tumors resulted in contrast changes within the bacteria-colonized tumors.

Conclusions: 

Our data suggest that colonization and gene expression by live vectors expressing bacterioferritin can be monitored by MRI due to contrast changes.
KW  - Blood-brain barrier
KW  - Gene-expression
KW  - Salmonella-typhimurium
KW  - Sugar-transport
KW  - Breast-tumors
KW  - MRI reporter
KW  - Iron-uptake
KW  - Proteins
KW  - Therapy
KW  - Mice
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-140920
VL  - 6
IS  - 10
ER  - 
TY  - JOUR
A1  - Borisjuk, Ljudmilla
A1  - Rolletschek, Hardy
A1  - Fuchs, Johannes
A1  - Melkus, Gerd
A1  - Neuberger, Thomas
T1  - Low and High Field Magnetic Resonance for \(in\) \(Vivo\) Analysis of Seeds
JF  - Materials
N2  - Low field NMR has been successfully used for the evaluation of seed composition and quality, but largely only in crop species. We show here that 1.5T NMR provides a reliable means for analysing the seed lipid fraction present in a wide range of species, where both the seed size and lipid concentration differed by >10 fold. Little use of high field NMR has been made in seed research to date, even though it potentially offers many opportunities for studying seed development, metabolism and storage. Here we demonstrate how 17.5T and 20T NMR can be applied to image seed structure, and analyse lipid and metabolite distribution. We suggest that further technical developments in NMR/MRI will facilitate significant advances in our understanding of seed biology.
KW  - Time-domain NMR
KW  - H-1-NMR spectroscopy
KW  - Soybean seeds
KW  - Human brain
KW  - Oil
KW  - Storage
KW  - Plants
KW  - Deterioration
KW  - Transport
KW  - Gradients
KW  - NMR
KW  - MRI
KW  - seed quality
KW  - Crop seed
KW  - lipid imaging
KW  - sucrose allocation
KW  - seed aging
KW  - (13)C
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-140910
VL  - 4
IS  - 8
ER  - 
TY  - JOUR
A1  - Sauer, C
A1  - Wießner, M
A1  - Schöll, A
A1  - Reinert, F
T1  - Observation of a molecule-metal interface charge transfer related feature by resonant photoelectron spectroscopy
JF  - New Journal of Physics
N2  - We report the discovery of a charge transfer (CT) related low binding energy feature at a molecule-metal interface by the application of resonant photoelectron spectroscopy (RPES). This interface feature is neither present for molecular bulk samples nor for the clean substrate. A detailed analysis of the spectroscopic signature of the low binding energy feature shows characteristics of electronic interaction not found in other electron spectroscopic techniques. Within a cluster model description this feature is assigned to a particular eigenstate of the photoionized system that is invisible in direct photoelectron spectroscopy but revealed in RPES through a relative resonant enhancement. Interpretations based on considering only the predominant character of the eigenstates explain the low binding energy feature by an occupied lowest unoccupied molecular orbital, which is either realized through CT in the ground or in the intermediate state. This reveals that molecule-metal CT is responsible for this feature. Consequently, our study demonstrates the sensitivity of RPES to electronic interactions and constitutes a new way to investigate CT at molecule-metal interfaces.
KW  - transfer dynamics
KW  - photoemission
KW  - states
KW  - interface
KW  - charge transfer
KW  - organic thin films
KW  - resonant photoelectron spectroscopy
KW  - energy
KW  - model calculation
KW  - NEXAFS spectroscopy
KW  - ce compounds
KW  - absorption
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-148672
VL  - 17
IS  - 043016
ER  - 
TY  - JOUR
A1  - Fuchs, F.
A1  - Stender, B.
A1  - Trupke, M.
A1  - Simin, D.
A1  - Pflaum, J.
A1  - Dyakonov, V.
A1  - Astakhov, G.V.
T1  - Engineering near-infrared single-photon emitters with optically active spins in ultrapure silicon carbide
JF  - Nature Communications
N2  - Vacancy-related centres in silicon carbide are attracting growing attention because of their appealing optical and spin properties. These atomic-scale defects can be created using electron or neutron irradiation; however, their precise engineering has not been demonstrated yet. Here, silicon vacancies are generated in a nuclear reactor and their density is controlled over eight orders of magnitude within an accuracy down to a single vacancy level. An isolated silicon vacancy serves as a near-infrared photostable single-photon emitter, operating even at room temperature. The vacancy spins can be manipulated using an optically detected magnetic resonance technique, and we determine the transition rates and absorption cross-section, describing the intensity-dependent photophysics of these emitters. The on-demand engineering of optically active spins in technologically friendly materials is a crucial step toward implementation of both maser amplifiers, requiring high-density spin ensembles, and qubits based on single spins.
KW  - nuclear magnetic resonance
KW  - coherent control
KW  - 4H
KW  - phosphorus
KW  - qubits
KW  - defects
KW  - entanglement
KW  - room temperature
KW  - vacancy
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-148502
VL  - 6
IS  - 7578
ER  - 
TY  - JOUR
A1  - Sessi, Paolo
A1  - Silkin, Vyacheslav M.
A1  - Nechaev, Ilya A.
A1  - Bathon, Thomas
A1  - El-Kareh, Lydia
A1  - Chulkov, Evgueni V.
A1  - Echenique, Pedro M.
A1  - Bode, Matthias
T1  - Direct observation of many-body charge density oscillations in a two-dimensional electron gas
JF  - Nature Communications
N2  - Quantum interference is a striking manifestation of one of the basic concepts of quantum mechanics: the particle-wave duality. A spectacular visualization of this effect is the standing wave pattern produced by elastic scattering of surface electrons around defects, which corresponds to a modulation of the electronic local density of states and can be imaged using a scanning tunnelling microscope. To date, quantum-interference measurements were mainly interpreted in terms of interfering electrons or holes of the underlying band-structure description. Here, by imaging energy-dependent standing-wave patterns at noble metal surfaces, we reveal, in addition to the conventional surface-state band, the existence of an 'anomalous' energy band with a well-defined dispersion. Its origin is explained by the presence of a satellite in the structure of the many-body spectral function, which is related to the acoustic surface plasmon. Visualizing the corresponding charge oscillations provides thus direct access to many-body interactions at the atomic scale.
KW  - scanning tunneling spectroscopy
KW  - acoustic surface plasmon
KW  - metal surfaces
KW  - Cu(111)
KW  - excitations
KW  - microscopy
KW  - local density
KW  - standing wave formation
KW  - states
KW  - steps
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-145246
VL  - 6
IS  - 8691
ER  - 
TY  - JOUR
A1  - Thierschmann, H
A1  - Arnold, F
A1  - Mittermüller, M
A1  - Maier, L
A1  - Heyn, C
A1  - Hansen, W
A1  - Buhmann, H
A1  - Molenkamp, L W
T1  - Thermal gating of charge currents with Coulomb coupled quantum dots
JF  - New Journal of Physics
N2  - We have observed thermal gating, i.e. electrostatic gating induced by hot electrons. The effect occurs in a device consisting of two capacitively coupled quantum dots. The double dot system is coupled to a hot electron reservoir on one side (QD1), while the conductance of the second dot (QD2) is monitored. When a bias across QD2 is applied we observe a current which is strongly dependent on the temperature of the heat reservoir. This current can be either enhanced or suppressed, depending on the relative energetic alignment of the QD levels. Thus, the system can be used to control a charge current by hot electrons.
KW  - oscillations
KW  - physics
KW  - quantum dot systems
KW  - Coulomb interaction
KW  - thermal gating
KW  - three terminal device
KW  - thermoelectrics
KW  - energy
KW  - thermopower
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-145196
VL  - 17
IS  - 113003
ER  - 
TY  - JOUR
A1  - Sacépé, Benjamin
A1  - Oostinga, Jeroen B.
A1  - Li, Jian
A1  - Ubaldini, Alberto
A1  - Couto, Nuno J. G.
A1  - Giannini, Enrico
A1  - Morpurgo, Alberto F.
T1  - Gate-tuned normal and superconducting transport at the surface of a topological insulator
JF  - Nature Communications
N2  - Three-dimensional topological insulators are characterized by the presence of a bandgap in their bulk and gapless Dirac fermions at their surfaces. New physical phenomena originating from the presence of the Dirac fermions are predicted to occur, and to be experimentally accessible via transport measurements in suitably designed electronic devices. Here we study transport through superconducting junctions fabricated on thin Bi2Se3 single crystals, equipped with a gate electrode. In the presence of perpendicular magnetic field B, sweeping the gate voltage enables us to observe the filling of the Dirac fermion Landau levels, whose character evolves continuously from electron- to hole-like. When B=0, a supercurrent appears, whose magnitude can be gate tuned, and is minimum at the charge neutrality point determined from the Landau level filling. Our results demonstrate how gated nano-electronic devices give control over normal and superconducting transport of Dirac fermions at an individual surface of a three-dimensional topological insulators.
KW  - Physical sciences
KW  - Condensed matter
KW  - Materials science
KW  - nanotechnology
Y1  - 2011
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-140175
VL  - 2
ER  - 
TY  - JOUR
A1  - Lee, Eun-Hye
A1  - Song, Jin-Dong
A1  - Han, Il-Ki
A1  - Chang, Soo-Kyung
A1  - Langer, Fabian
A1  - Höfling, Sven
A1  - Forchel, Alfred
A1  - Kamp, Martin
A1  - Kim, Jong-Su
T1  - Structural and optical properties of position-retrievable low-density GaAs droplet epitaxial quantum dots for application to single photon sources with plasmonic optical coupling
JF  - Nanoscale Research Letters
N2  - The position of a single GaAs quantum dot (QD), which is optically active, grown by low-density droplet epitaxy (DE) (approximately 4 QDs/μm\(^{2}\)), was directly observed on the surface of a 45-nm-thick Al\(_{0.3}\)Ga\(_{0.7}\)As capping layer. The thin thickness of AlGaAs capping layer is useful for single photon sources with plasmonic optical coupling. A micro-photoluminescence for GaAs DE QDs has shown exciton/biexciton behavior in the range of 1.654 to 1.657 eV. The direct observation of positions of low-density GaAs DE QDs would be advantageous for mass fabrication of devices that use a single QD, such as single photon sources.
KW  - quantum dot
KW  - droplet epitaxy
KW  - micro-photoluminescence
KW  - single photon
KW  - GaAs
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-143692
VL  - 10
IS  - 114
ER  - 
TY  - JOUR
A1  - Suchomel, H.
A1  - Brodbeck, S.
A1  - Liew, T. C. H.
A1  - Amthor, M.
A1  - Klaas, M.
A1  - Klembt, S.
A1  - Kamp, M.
A1  - Höfling, S.
A1  - Schneider, C.
T1  - Prototype of a bistable polariton field-effect transistor switch
JF  - Scientific Reports
N2  - Microcavity exciton polaritons are promising candidates to build a new generation of highly nonlinear and integrated optoelectronic devices. Such devices range from novel coherent light emitters to reconfigurable potential landscapes for electro-optical polariton-lattice based quantum simulators as well as building blocks of optical logic architectures. Especially for the latter, the strongly interacting nature of the light-matter hybrid particles has been used to facilitate fast and efficient switching of light by light, something which is very hard to achieve with weakly interacting photons. We demonstrate here that polariton transistor switches can be fully integrated in electro-optical schemes by implementing a one-dimensional polariton channel which is operated by an electrical gate rather than by a control laser beam. The operation of the device, which is the polariton equivalent to a field-effect transistor, relies on combining electro-optical potential landscape engineering with local exciton ionization to control the scattering dynamics underneath the gate. We furthermore demonstrate that our device has a region of negative differential resistance and features a completely new way to create bistable behavior.
KW  - materials for optics
KW  - nanoscience and technology
KW  - optics and photonics
KW  - semiconductors
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-158323
VL  - 7
IS  - 5114
ER  - 
TY  - JOUR
A1  - Herold, Volker
A1  - Herz, Stefan
A1  - Winter, Patrick
A1  - Gutjahr, Fabian Tobias
A1  - Andelovic, Kristina
A1  - Bauer, Wolfgang Rudolf
A1  - Jakob, Peter Michael
T1  - Assessment of local pulse wave velocity distribution in mice using k-t BLAST PC-CMR with semi-automatic area segmentation.
JF  - Journal of Cardiovascular Magnetic Resonance
N2  - Background:
Local aortic pulse wave velocity (PWV) is a measure for vascular stiffness and has a predictive value for cardiovascular events. Ultra high field CMR scanners allow the quantification of local PWV in mice, however these systems are yet unable to monitor the distribution of local elasticities.
Methods:
In the present study we provide a new accelerated method to quantify local aortic PWV in mice with phase-contrast cardiovascular magnetic resonance imaging (PC-CMR) at 17.6 T. Based on a k-t BLAST (Broad-use Linear Acquisition Speed-up Technique) undersampling scheme, total measurement time could be reduced by a factor of 6. The fast data acquisition enables to quantify the local PWV at several locations along the aortic blood vessel based on the evaluation of local temporal changes in blood flow and vessel cross sectional area. To speed up post processing and to eliminate operator bias, we introduce a new semi-automatic segmentation algorithm to quantify cross-sectional areas of the aortic vessel. The new methods were applied in 10 eight-month-old mice (4 C57BL/6J-mice and 6 ApoE\(^{(-/-)}\)-mice) at 12 adjacent locations along the abdominal aorta.
Results:
Accelerated data acquisition and semi-automatic post-processing delivered reliable measures for the local PWV, similiar to those obtained with full data sampling and manual segmentation. No statistically significant differences of the mean values could be detected for the different measurement approaches. Mean PWV values were elevated for the ApoE\(^{(-/-)}\)-group compared to the C57BL/6J-group (3.5 ± 0.7 m/s vs. 2.2 ± 0.4 m/s, p < 0.01). A more heterogeneous PWV-distribution in the ApoE \(^{(-/-)}\)-animals could be observed compared to the C57BL/6J-mice, representing the local character of lesion development in atherosclerosis.
Conclusion:
In the present work, we showed that k-t BLAST PC-MRI enables the measurement of the local PWV distribution in the mouse aorta. The semi-automatic segmentation method based on PC-CMR data allowed rapid determination of local PWV. The findings of this study demonstrate the ability of the proposed methods to non-invasively quantify the spatial variations in local PWV along the aorta of ApoE\(^{(-/-)}\)-mice as a relevant model of atherosclerosis.
KW  - pulse wave velocity
KW  - ApoE\(^{(-/-)}\)
KW  - magnetic resonance imaging
KW  - phase contrast
Y1  - 2017
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-157696
VL  - 19
IS  - 77
ER  - 
TY  - JOUR
A1  - Reiter, Theresa
A1  - Gensler, Daniel
A1  - Ritter, Oliver
A1  - Weiss, Ingo
A1  - Geistert, Wolfgang
A1  - Kaufmann, Ralf
A1  - Hoffmeister, Sabine
A1  - Friedrich, Michael T.
A1  - Wintzheimer, Stefan
A1  - Düring, Markus
A1  - Nordbeck, Peter
A1  - Jakob, Peter M.
A1  - Ladd, Mark E.
A1  - Quick, Harald H.
A1  - Bauer, Wolfgang R.
T1  - Direct cooling of the catheter tip increases safety for CMR-guided electrophysiological procedures
JF  - Journal of Cardiovascular Magnetic Resonance
N2  - Background: One of the safety concerns when performing electrophysiological (EP) procedures under magnetic resonance (MR) guidance is the risk of passive tissue heating due to the EP catheter being exposed to the radiofrequency (RF) field of the RF transmitting body coil. Ablation procedures that use catheters with irrigated tips are well established therapeutic options for the treatment of cardiac arrhythmias and when used in a modified mode might offer an additional system for suppressing passive catheter heating. 
Methods: A two-step approach was chosen. Firstly, tests on passive catheter heating were performed in a 1.5 T Avanto system (Siemens Healthcare Sector, Erlangen, Germany) using a ASTM Phantom in order to determine a possible maximum temperature rise. Secondly, a phantom was designed for simulation of the interface between blood and the vascular wall. The MR-RF induced temperature rise was simulated by catheter tip heating via a standard ablation generator. Power levels from 1 to 6 W were selected. Ablation duration was 120 s with no tip irrigation during the first 60 s and irrigation at rates from 2 ml/min to 35 ml/min for the remaining 60 s (Biotronik Qiona Pump, Berlin, Germany). The temperature was measured with fluoroscopic sensors (Luxtron, Santa Barbara, CA, USA) at a distance of 0 mm, 2 mm, 4 mm, and 6 mm from the catheter tip. Results: A maximum temperature rise of 22.4 degrees C at the catheter tip was documented in the MR scanner. This temperature rise is equivalent to the heating effect of an ablator's power output of 6 W at a contact force of the weight of 90 g (0.883 N). The catheter tip irrigation was able to limit the temperature rise to less than 2 degrees C for the majority of examined power levels, and for all examined power levels the residual temperature rise was less than 8 degrees C. 
Conclusion: Up to a maximum of 22.4 degrees C, the temperature rise at the tissue surface can be entirely suppressed by using the catheter's own irrigation system. The irrigated tip system can be used to increase MR safety of EP catheters by suppressing the effects of unwanted passive catheter heating due to RF exposure from the MR scanner.
KW  - EP Procedures
KW  - radiofrequency ablation
KW  - contact force
KW  - lesion size
KW  - MRI
KW  - temperature
KW  - tissue
KW  - wires
KW  - model
KW  - ablation
KW  - safety
KW  - catheter tip
KW  - MR guidance
Y1  - 2012
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-134927
VL  - 14
IS  - 12
ER  - 
TY  - JOUR
A1  - Ma, Eric Yue
A1  - Calvo, M. Reyes
A1  - Wang, Jing
A1  - Lian, Biao
A1  - Mühlbauer, Mathias
A1  - Brüne, Christoph
A1  - Cui, Yong-Tao
A1  - Lai, Keji
A1  - Kundhikanjana, Worasom
A1  - Yang, Yongliang
A1  - Baenninger, Matthias
A1  - König, Markus
A1  - Ames, Christopher
A1  - Buhmann, Hartmut
A1  - Leubner, Philipp
A1  - Molenkamp, Laurens W.
A1  - Zhang, Shou-Cheng
A1  - Goldhaber-Gordon, David
A1  - Kelly, Michael A.
A1  - Shen, Zhi-Xun
T1  - Unexpected edge conduction in mercury telluride quantum wells under broken time-reversal symmetry
JF  - Nature Communications
N2  - The realization of quantum spin Hall effect in HgTe quantum wells is considered a milestone in the discovery of topological insulators. Quantum spin Hall states are predicted to allow current flow at the edges of an insulating bulk, as demonstrated in various experiments. A key prediction yet to be experimentally verified is the breakdown of the edge conduction under broken time-reversal symmetry. Here we first establish a systematic framework for the magnetic field dependence of electrostatically gated quantum spin Hall devices. We then study edge conduction of an inverted quantum well device under broken time-reversal symmetry using microwave impedance microscopy, and compare our findings to a noninverted device. At zero magnetic field, only the inverted device shows clear edge conduction in its local conductivity profile, consistent with theory. Surprisingly, the edge conduction persists up to 9 T with little change. This indicates physics beyond simple quantum spin Hall model, including material-specific properties and possibly many-body effects.
KW  - topological insulators
KW  - surface states
KW  - HgTe
KW  - Hg1-xCdxTe
KW  - vacancies
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-143185
VL  - 6
IS  - 7252
ER  - 
TY  - JOUR
T1  - Search for a CP-odd Higgs boson decaying to Zh in pp   collisions at \(\sqrt{s}\)=8 TeV with the ATLAS detector
JF  - Physics Letters B
N2  - A search for a heavy, CP-odd Higgs boson, A, decaying into a Z boson and a 125 GeV Higgs boson, h, with the ATLAS detector at the LHC is presented. The search uses proton–proton collision data at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 20.3 fb\(^{-1}\). Decays of CP-even h bosons to ττ or bb pairs with the Z   boson decaying to electron or muon pairs are considered, as well as h→bb decays with the Z boson decaying to neutrinos. No evidence for the production of an A   boson in these channels is found and the 95% confidence level upper limits derived for σ(gg→A)×BR(A→Zh)×BR(h→f\(\bar{f}\)) are 0.098–0.013 pb for f=τ and 0.57–0.014 pb for f=b in a range of m\(_{A}\)=220–1000 GeVmA=220–1000 GeV. The results are combined and interpreted in the context of two-Higgs-doublet models.
KW  - BSM Higgs boson
KW  - ATLAS
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-143050
VL  - 744
ER  - 
TY  - JOUR
A1  - Charnukha, A.
A1  - Thirupathaiah, S.
A1  - Zabolotnyy, V. B.
A1  - Büchner, B.
A1  - Zhigadlo, N. D.
A1  - Batlogg, B.
A1  - Yaresko, A. N.
A1  - Borisenko, S. V.
T1  - Interaction-induced singular Fermi surface in a high-temperature oxypnictide superconductor
JF  - Scientific Reports
N2  - In the family of iron-based superconductors, LaFeAsO-type materials possess the simplest electronic structure due to their pronounced two-dimensionality. And yet they host superconductivity with the highest transition temperature T\(_{c}\)\(\approx\)55K. Early theoretical predictions of their electronic structure revealed multiple large circular portions of the Fermi surface with a very good geometrical overlap (nesting), believed to enhance the pairing interaction and thus superconductivity. The prevalence of such large circular features in the Fermi surface has since been associated with many other iron-based compounds and has grown to be generally accepted in the field. In this work we show that a prototypical compound of the 1111-type, SmFe\(_{0.92}\)Co\(_{0.08}\)AsO, is at odds with this description and possesses a distinctly different Fermi surface, which consists of two singular constructs formed by the edges of several bands, pulled to the Fermi level from the depths of the theoretically predicted band structure by strong electronic interactions. Such singularities dramatically affect the low-energy electronic properties of the material, including superconductivity. We further argue that occurrence of these singularities correlates with the maximum superconducting transition temperature attainable in each material class over the entire family of iron-based superconductors.
KW  - electronic structure
KW  - photoemission spectroscopy
KW  - iron pnictides
KW  - chalcogenides
KW  - ARPES
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-151987
VL  - 5
IS  - 10392
ER  - 
TY  - JOUR
A1  - Zhang, Xin
A1  - Wu, Wei
A1  - Li, Gang
A1  - Wen, Lin
A1  - Sun, Qing
A1  - Ji, An-Chun
T1  - Phase diagram of interacting Fermi gas in spin-orbit coupled square lattices
JF  - New Journal of Physics
N2  - The spin-orbit (SO) coupled optical lattices have attracted considerable interest. In this paper, we investigate the phase diagram of the interacting Fermi gas with Rashba-type spin-orbit coupling (SOC) on a square optical lattice. The phase diagram is investigated in a wide range of atomic interactions and SOC strength within the framework of the cluster dynamical mean-field theory (CDMFT). We show that the interplay between the atomic interactions and SOC results in a rich phase diagram. In the deep Mott insulator regime, the SOC can induce diverse spin ordered phases. Whereas near the metal-insulator transition (MIT), the SOC tends to destroy the conventional antiferromagnetic fluctuations, giving rise to distinctive features of the MIT. Furthermore, the strong fluctuations arising from SOC may destroy the magnetic orders and trigger an order to disorder transition in close proximity of the MIT.
KW  - ultracold
KW  - hubbard-model
KW  - physics transition
KW  - metal-insulator transition
KW  - cluster dynamical mean-field theory
KW  - atomic gases
KW  - mean-field theory
KW  - mott insulator
KW  - optical lattice
KW  - weak ferromagnetism
KW  - quantum gases
KW  - superfluid
KW  - spin-orbit coupling
Y1  - 2015
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-151475
VL  - 17
IS  - 073036
ER  -