@article{WurdackLundtKlaasetal.2017,
  author    = {Wurdack, Matthias and Lundt, Nils and Klaas, Martin and Baumann, Vasilij and Kavokin, Alexey V. and H{\"o}fling, Sven and Schneider, Christian},
  title     = {Observation of hybrid Tamm-plasmon exciton-polaritons with GaAs quantum wells and a MoSe\(_{2}\) monolayer},
  series = {Nature Communications},
  volume    = {8},
  journal   = {Nature Communications},
  number    = {259},
  doi       = {10.1038/s41467-017-00155-w},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-170480},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@article{TriphanJobstAnjorinetal.2017,
  author    = {Triphan, Simon M. F. and Jobst, Bertram J. and Anjorin, Angela and Sedlaczek, Oliver and Wolf, Ursula and Terekhov, Maxim and Hoffmann, Christian and Ley, Sebastian and D{\"u}ber, Christoph and Biederer, J{\"u}rgen and Kauczor, Hans-Ulrich and Jakob, Peter M. and Wielp{\"u}tz, Mark O.},
  title     = {Reproducibility and comparison of oxygen-enhanced T\(_1\) quantification in COPD and asthma patients},
  series = {PLoS ONE},
  volume    = {12},
  journal   = {PLoS ONE},
  number    = {2},
  doi       = {10.1371/journal.pone.0172479},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-171833},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@phdthesis{Then2017,
  author    = {Then, Patrick},
  title     = {Waveguide-based single molecule detection in flow},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-140548},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {In this work fluorescence-based single molecule detection at low concetration is investigated, with an emphasis on the usage of active transport and waveguides. Active transport allows to overcome the limits of diffusion-based systems in terms of the lowest detectable threshold of concentration. The effect of flow in single molecule experiments is investigated and a theoretical model is derived for laminar flow. Waveguides on the other hand promise compact detection schemes and show great potential for their possible integration into lab-on-a-chip applications. Their properties in single molecule experiments are analyzed with help of a method based on the reciprocity theorem of electromagnetic theory.},
  subject      = {Optik},
  language  = {en}
}
@article{SanchezThierschmannMolenkamp2017,
  author    = {S{\´a}nchez, Rafael and Thierschmann, Holger and Molenkamp, Laurens W.},
  title     = {Single-electron thermal devices coupled to a mesoscopic gate},
  series = {New Journal of Physics},
  volume    = {19},
  journal   = {New Journal of Physics},
  doi       = {10.1088/1367-2630/aa8b94},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172982},
  year      = {2017},
  abstract  = {We theoretically investigate the propagation of heat currents in a three-terminal quantum dot engine. Electron-electron interactions introduce state-dependent processes which can be resolved by energy-dependent tunneling rates. We identify the relevant transitions which define the operation of the system as a thermal transistor or a thermal diode. In the former case, thermal-induced charge fluctuations in the gate dot modify the thermal currents in the conductor with suppressed heat injection, resulting in huge amplification factors and the possible gating with arbitrarily low energy cost. In the latter case, enhanced correlations of the state-selective tunneling transitions redistribute heat flows giving high rectification coefficients and the unexpected cooling of one conductor terminal by heating the other one. We propose quantum dot arrays as a possible way to achieve the extreme tunneling asymmetries required for the different operations.},
  language  = {en}
}
@article{SyperekAndrzejewskiRudnoRudzińskietal.2017,
  author    = {Syperek, M. and Andrzejewski, J. and Rudno-Rudziński, W. and Maryński, A. and Sȩk, G. and Misiewicz, J. and Reithmaier, J. P. and Somers, A. and H{\"o}fling, S.},
  title     = {The issue of 0D-like ground state isolation in GaAs- and InP-based coupled quantum dots-quantum well systems},
  series = {Journal of Physics: Conference Series},
  volume    = {906},
  journal   = {Journal of Physics: Conference Series},
  number    = {1},
  issn      = {1742-6588},
  doi       = {10.1088/1742-6596/906/1/012019},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-262876},
  year      = {2017},
  abstract  = {The issue of quantum mechanical coupling between a semiconductor quantum dot and a quantum well is studied in two families of GaAs- and InP- based structures at cryogenic temperatures. It is shown that by tuning the quantum well parameters one can strongly disturb the 0D-character of the coupled system ground state, initially located in a dot. The out-coupling of either an electron or a hole state from the quantum dot confining potential is viewed by a significant elongation of the photoluminescence decay time constant. Band structure calculations show that in the GaAs-based coupled system at its ground state a hole remains isolated in the dot, whereas an electron gets delocalized towards the quantum well. The opposite picture is built for the ground state of a coupled system based on InP.},
  language  = {en}
}
@phdthesis{Swimm2017,
  author    = {Swimm, Katrin},
  title     = {Experimentelle und theoretische Untersuchungen zur gasdruckabh{\"a}ngigen W{\"a}rmeleitf{\"a}higkeit von por{\"o}sen Materialien},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-153887},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {Als W{\"a}rmed{\"a}mmstoffe werden {\"u}blicherweise makropor{\"o}se Stoffsysteme wie Sch{\"a}ume, Pul-versch{\"u}ttungen, Faservliese und - wolle eingesetzt. Zus{\"a}tzlich finden mikro- und mesopor{\"o}se D{\"a}mmstoffe wie Aerogele Anwendung. Um effiziente W{\"a}rmed{\"a}mmstoffe entwickeln zu k{\"o}nnen, muss der Gesamtw{\"a}rmetransport in por{\"o}sen Materialien verstanden werden. Die ein-zelnen W{\"a}rmetransport-Mechanismen Festk{\"o}rperw{\"a}rmeleitung, Gasw{\"a}rmeleitung und W{\"a}rme-strahlung k{\"o}nnen zuverl{\"a}ssig analytisch beschrieben werden. Bei manchen por{\"o}sen Materialien liefert jedoch auch eine Wechselwirkung zwischen den verschiedenen W{\"a}rmetransport-Mechanismen, d.h. die Kopplung von Festk{\"o}rper- und Gasw{\"a}rmeleitung, einen hohen Beitrag zur Gesamtw{\"a}rmeleitf{\"a}higkeit. Wie hoch dieser Kopplungseffekt bei einer bestimmten Probe ausf{\"a}llt, kann bisher schwer abgesch{\"a}tzt werden. Um den Kopplungseffekt von Festk{\"o}rper- und Gasw{\"a}rmeleitung besser zu verstehen, sind sowohl experimentelle als auch theoretische Untersuchungen an verschiedenen por{\"o}sen Stoffsystemen erforderlich. Zus{\"a}tzlich kann ein zuverl{\"a}ssiges theoretisches Modell dazu beitragen, die mittlere Porengr{\"o}ße von por{\"o}sen Mate-rialien zerst{\"o}rungsfrei anhand von gasdruckabh{\"a}ngigen W{\"a}rmeleitf{\"a}higkeitsmessungen zu bestimmen. Als Modellsystem f{\"u}r die experimentellen Untersuchungen wurde der hochpor{\"o}se Feststoff Aerogel verwendet, da seine strukturellen Eigenschaften wie Porengr{\"o}ße und Dichte w{\"a}hrend der Synthese gut eingestellt werden k{\"o}nnen. Es wurden Resorcin-Formaldehyd-Aerogele mit mittleren Porengr{\"o}ßen von etwa 600 nm, 1 µm und 8 µm sowie daraus mittels Pyrolyse abge-leitete Kohlenstoff-Aerogele synthetisiert und jeweils hinsichtlich ihrer Struktur und W{\"a}rme-leitf{\"a}higkeiten experimentell charakterisiert. Die Gesamtw{\"a}rmeleitf{\"a}higkeiten dieser Aerogele wurden f{\"u}r verschiedene Gasatmosph{\"a}ren (Kohlenstoffdioxid, Argon, Stickstoff und Helium) in Abh{\"a}ngigkeit vom Gasdruck durch das Hitzdraht-Verfahren bestimmt. Hierf{\"u}r wurde der Messbereich der Hitzdraht-Apparatur des ZAE Bayern mittels einer Druckzelle auf 10 MPa erweitert. Die Messergebnisse zeigen, dass bei allen Aerogel-Proben Festk{\"o}rper- und Gasw{\"a}r-meleitung einen deutlichen Kopplungsbeitrag liefern: Die gemessenen gasdruckabh{\"a}ngigen W{\"a}rmeleitf{\"a}higkeiten sind um Faktor 1,3 bis 3,3 h{\"o}her als die entsprechenden reinen Gas-w{\"a}rmeleitf{\"a}higkeiten. Die jeweilige H{\"o}he h{\"a}ngt sowohl vom verwendeten Gas (Gasw{\"a}rmeleitf{\"a}higkeit) als auch vom Aerogeltyp (Festk{\"o}rperw{\"a}rmeleitf{\"a}higkeit und Festk{\"o}rperstruktur) ab. Ein stark vernetzter Festk{\"o}rper verursacht beispielsweise einen niedrigeren Kopplungsbei-trag als ein weniger stark vernetzter Festk{\"o}rper. Andererseits wurde die gasdruckabh{\"a}ngige W{\"a}rmeleitf{\"a}higkeit von Melaminharzschaum - einem flexiblen, offenporigen und hochpor{\"o}sen Material - in einer evakuierbaren Zwei-Plattenapparatur unter Stickstoff-Atmosph{\"a}re bestimmt. Das Material zeichnet sich dadurch aus, dass die Addition der Einzelw{\"a}rmeleitf{\"a}higkeiten gut erf{\"u}llt ist, d.h. kein Kopplungsef-fekt auftritt. Allerdings konnte gezeigt werden, dass die gestauchte und damit unregelm{\"a}ßige Struktur von Melaminharzschaum die Kopplung von Festk{\"o}rper- und Gasw{\"a}rmeleitung deut-lich beg{\"u}nstigt. Je st{\"a}rker die Melaminharzschaumprobe komprimiert wird, umso st{\"a}rker f{\"a}llt der Kopplungseffekt aus. Bei einer Kompression um 84 \% ist beispielsweise die gemessene gasdruckabh{\"a}ngige W{\"a}rmeleitf{\"a}higkeit bei 0,1 MPa um ca. 17 \% gegen{\"u}ber der effektiven W{\"a}rmeleitf{\"a}higkeit von freiem Stickstoff erh{\"o}ht. Die experimentellen Untersuchungen wurden durch theoretische Betrachtungen erg{\"a}nzt. Zum einen wurde die Kopplung von Festk{\"o}rper- und Gasw{\"a}rmeleitung anhand einer Serienschal-tung der thermischen Widerst{\"a}nde von Festk{\"o}rper- und Gasphase dargestellt, um die Abh{\"a}n-gigkeit von verschiedenen Parametern zu untersuchen. Dadurch konnte gezeigt werden, dass der Kopplungsterm stets von den Verh{\"a}ltnissen aus Festk{\"o}rper- und Gasw{\"a}rmeleitf{\"a}higkeit sowie aus den geometrischen Parametern beider Phasen abh{\"a}ngt. Des Weiteren wurden mit dem Computerprogramm HEAT2 Finite-Differenzen-Simulationen an Modellstrukturen durchgef{\"u}hrt, die f{\"u}r por{\"o}se Stoffsysteme, insbesondere Aerogel, charakteristisch sind (Stege, H{\"a}lse, Windungen und tote Enden). Die simulierten gasdruckabh{\"a}ngigen W{\"a}rmeleitf{\"a}higkeiten zeigen deutlich, dass die Festk{\"o}rperstruktur mit der geringsten Vernetzung, d.h. das tote Ende, am meisten zur Kopplung von Festk{\"o}rper- und Gasw{\"a}rmeleitung beitr{\"a}gt. Dies korre-liert mit den experimentellen Ergebnissen. Dar{\"u}ber hinaus kann man erkennen, dass die Ge-samtw{\"a}rmeleitf{\"a}higkeit eines schlecht vernetzten por{\"o}sen Systems, wo also ein hoher Kopp-lungseffekt (Serienschaltung) auftritt, niemals gr{\"o}ßer wird als die eines gut vernetzten Sys-tems mit gleicher Porosit{\"a}t, wo haupts{\"a}chlich paralleler W{\"a}rmetransport durch beide Phasen stattfindet. Schließlich wurden drei Modelle entwickelt bzw. modifiziert, um die gasdruckabh{\"a}ngige W{\"a}rmeleitf{\"a}higkeit von por{\"o}sen Stoffsystemen theoretisch beschreiben zu k{\"o}nnen. Zun{\"a}chst wurde ein f{\"u}r Kugelsch{\"u}ttungen entwickeltes Modell f{\"u}r Aerogel angepasst, d.h. Kopplung von Festk{\"o}rper- und Gasw{\"a}rmeleitung wurde nur in den L{\"u}cken zwischen zwei benachbarten Partikeln ber{\"u}cksichtigt. Ein Vergleich mit den Messkurven zeigt, dass der ermittelte Kopplungsterm zu gering ausf{\"a}llt. Daher wurde ein bereits existierendes Aerogelmodell mit kubischer Einheitszelle, welches zus{\"a}tzlich Kopplung zwischen den einzelnen Partikelstr{\"a}ngen beinhaltet, verbessert. Auch dieses Modell liefert keine zufriedenstellende {\"U}bereinstimmung mit den Messwerten, denn der Kopplungsbeitrag wird immer noch untersch{\"a}tzt. Das liegt daran, dass die gew{\"a}hlte regelm{\"a}ßige kubische Struktur f{\"u}r Aerogel zu ungenau ist. So geht bei der Berechnung des Kopplungsterms der bereits erw{\"a}hnte hohe Beitrag durch tote Enden (und auch Windungen) verloren. Erfahrungsgem{\"a}ß k{\"o}nnen jedoch alle f{\"u}r Aerogel erhaltenen gasdruckabh{\"a}ngigen Messkurven mit dem sogenannten Skalierungsmodell relativ gut beschrieben werden. Das entspricht dem Knudsen-Modell f{\"u}r reine Gasw{\"a}rmeleitung, welches mit einem konstanten Faktor skaliert wird. Die Anwendung dieses einfachen Modells auf die Messdaten hat gezeigt, dass die Akkommodationskoeffizienten von Helium in Aerogel deut-lich h{\"o}her sind als die Literaturwerte (ca. 0,3 auf Metalloberfl{\"a}chen): In den vermessenen RF- und Kohlenstoff-Aerogelen lassen sich Akkommodationskoeffizienten nahe 1 f{\"u}r Helium ab-leiten. Dar{\"u}ber hinaus ist das Skalierungsmodell gut geeignet, die mittleren Porengr{\"o}ßen por{\"o}ser Materialien zuverl{\"a}ssig aus gasdruckabh{\"a}ngig gemessenen W{\"a}rmeleitf{\"a}higkeitskurven zu bestimmen. Dies stellt somit eine unkomplizierte und zerst{\"o}rungsfreie Charakterisierungsmethode dar.},
  subject      = {W{\"a}rmeleitf{\"a}higkeit},
  language  = {de}
}
@article{SuchomelBrodbeckLiewetal.2017,
  author    = {Suchomel, H. and Brodbeck, S. and Liew, T. C. H. and Amthor, M. and Klaas, M. and Klembt, S. and Kamp, M. and H{\"o}fling, S. and Schneider, C.},
  title     = {Prototype of a bistable polariton field-effect transistor switch},
  series = {Scientific Reports},
  volume    = {7},
  journal   = {Scientific Reports},
  number    = {5114},
  doi       = {10.1038/s41598-017-05277-1},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-158323},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@article{StrasserSchrauthDembskietal.2017,
  author    = {Straßer, Marion and Schrauth, Joachim H. X. and Dembski, Sofia and Haddad, Daniel and Ahrens, Bernd and Schweizer, Stefan and Christ, Bastian and Cubukova, Alevtina and Metzger, Marco and Walles, Heike and Jakob, Peter M. and Sextl, Gerhard},
  title     = {Calcium fluoride based multifunctional nanoparticles for multimodal imaging},
  series = {Beilstein Journal of Nanotechnology},
  volume    = {8},
  journal   = {Beilstein Journal of Nanotechnology},
  doi       = {10.3762/bjnano.8.148},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-170657},
  pages     = {1484-1493},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@phdthesis{Stender2017,
  author    = {Stender, Benedikt},
  title     = {Einzelphotonenemitter und ihre Wechselwirkung mit Ladungstr{\"a}gern in organischen Leuchtdioden},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-150913},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {In dieser Arbeit wird die Photophysik von Einzelphotonenemittern unterschiedlicher Materialklassen, wie Fehlstellen in Diamant und Siliziumcarbid sowie organischer Molek{\"u}le bei Raumtemperatur untersucht. Zu diesem Zweck wurde ein hochaufl{\"o}sendes konfokales Mikroskop konzipiert und konstruiert, welches die optische Detektion einzelner Quantensysteme erm{\"o}glicht. Zus{\"a}tzlich werden verschiedene Methoden wie die Rotationsbeschichtung, das Inkjet-Printing und das Inkjet-Etching in Bezug auf die Reproduzierbarkeit und Strukturierbarkeit von organischen Leuchtdioden (OLEDs) verglichen. Im weiteren Verlauf werden die optoelektronischen Prozesse in dotierten OLEDs untersucht, ausgehend von hohen Dotierkonzentrationen bis hin zur Dotierung mit einzelnen Molek{\"u}len. Dadurch kann die Exzitonen-Ladungstr{\"a}ger Wechselwirkung auf und in der Umgebung von r{\"a}umlich isolierten Molek{\"u}len analysiert werden.},
  subject      = {Einzelphotonenemission},
  language  = {de}
}
@article{SkryabinKartashovEgorovetal.2017,
  author    = {Skryabin, D.V. and Kartashov, Y.V. and Egorov, O.A. and Sich, M. and Chana, J.K. and Tapia Rodriguez, L.E. and Walker, P.M. and Clarke, E. and Royall, B. and Skolnick, M.S. and Krizhanovskii, D.N.},
  title     = {Backward Cherenkov radiation emitted by polariton solitons in a microcavity wire},
  series = {Nature Communications},
  volume    = {8},
  journal   = {Nature Communications},
  doi       = {10.1038/s41467-017-01751-6},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-173046},
  year      = {2017},
  abstract  = {Exciton-polaritons in semiconductor microcavities form a highly nonlinear platform to study a variety of effects interfacing optical, condensed matter, quantum and statistical physics. We show that the complex polariton patterns generated by picosecond pulses in microcavity wire waveguides can be understood as the Cherenkov radiation emitted by bright polariton solitons, which is enabled by the unique microcavity polariton dispersion, which has momentum intervals with positive and negative group velocities. Unlike in optical fibres and semiconductor waveguides, we observe that the microcavity wire Cherenkov radiation is predominantly emitted with negative group velocity and therefore propagates backwards relative to the propagation direction of the emitting soliton. We have developed a theory of the microcavity wire polariton solitons and of their Cherenkov radiation and conducted a series of experiments, where we have measured polariton-soliton pulse compression, pulse breaking and emission of the backward Cherenkov radiation.},
  language  = {en}
}
@phdthesis{Simin2017,
  author    = {Simin, Dmitrij},
  title     = {Quantum Sensing with Highly Coherent Spin Centers in Silicon Carbide},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-156199},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {In the present work, the energetic structure and coherence properties of the silicon vacancy point defect in the technologically important material silicon carbide are extensively studied by the optically detected magnetic resonance (ODMR) technique in order to verify its high potential for various quantum applications. In the spin vacancy, unique attributes are arising from the C3v symmetry and the spin-3/2 state, which are not fully described by the standard Hamiltonian of the uniaxial model. Therefore, an advanced Hamiltonian, describing well the appearing phenomena is established and the relevant parameters are experimentally determined. Utilizing these new accomplishments, several quantum metrology techniques are proposed. First, a vector magnetometry scheme, utilizing the appearance of four ODMR lines, allows for simultaneous detection of the magnetic field strength and the tilting angle of the magnetic field from the symmetry axis of the crystal. The second magnetometry protocol utilizes the appearance of energetic level anticrossings (LAC) in the ground state (GS) energy levels. Relying only on the change in photoluminescence in the vicinity of this GSLACs, this all-optical method does not require any radio waves and hence provides a much easier operation with less error sources as for the common magnetometry schemes utilizing quantum points. A similar all-optical method is applied for temperature sensing, utilizing the thermal shift of the zero field splitting and consequently the anticrossing in the excited state (ES). Since the GSLACs show no dependence on temperature, the all-optical magnetometry and thermometry (utilizing the ESLACs) can be conducted subsequently on the same defect. In order to quantify the achievable sensitivity of quantum metrology, as well as to prove the potential of the Si-vacancy in SiC for quantum processing, the coherence properties are investigated by the pulsed ODMR technique. The spin-lattice relaxation time T1 and the spin-spin relaxation time T2 are thoroughly analyzed for their dependence on the external magnetic field and temperature. For actual sensing implementations, it is crucial to obtain the best signal-to-noise ratio without loss in coherence time. Therefore, the irradiation process, by which the defects are created in the crystal, plays a decisive role in the device performance. In the present work, samples irradiated with electrons or neutrons with different fluences and energies, producing different defect densities, are analyzed in regard to their T1 and T2 times at room temperature. Last but not least, a scheme to substantially prolong the T2 coherence time by locking the spin polarization with the dynamic decoupling Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence is applied.},
  subject      = {Siliciumcarbid},
  language  = {en}
}
@article{ShamimMahapatraScappuccietal.2017,
  author    = {Shamim, Saquib and Mahapatra, S. and Scappucci, G. and Klesse, W. M. and Simmons, M. Y. and Ghosh, Arindam},
  title     = {Dephasing rates for weak localization and universal conductance fluctuations in two dimensional Si: P and Ge: P δ-layers},
  series = {Scientific Reports},
  volume    = {7},
  journal   = {Scientific Reports},
  number    = {46670},
  doi       = {10.1038/srep46670},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-170934},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@article{RyczkoMisiewiczHoflingetal.2017,
  author    = {Ryczko, K. and Misiewicz, J. and Hofling, S. and Kamp, M. and Sęk, G.},
  title     = {Optimizing the active region of interband cascade lasers for passive mode-locking},
  series = {AIP Advances},
  volume    = {7},
  journal   = {AIP Advances},
  number    = {1},
  doi       = {10.1063/1.4973937},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-181790},
  year      = {2017},
  abstract  = {The work proposes possible designs of active regions for a mode-locked interband cascade laser emitting in the mid infrared. For that purpose we investigated the electronic structure properties of respectively modified GaSb-based type II W-shaped quantum wells, including the effect of external bias in order to simultaneously fulfil the requirements for both the absorber as well as the gain sections of a device. The results show that introducing multiple InAs layers in type II InAs/GaInSb quantum wells or introducing a tensely-strained GaAsSb layer into "W-shaped" type II QWs offers significant difference in optical transitions' oscillator strengths (characteristic lifetimes) of the two oppositely polarized parts of such a laser, being promising for utilization in mode-locked devices.},
  language  = {en}
}
@article{RudnoRudzińskiSyperekAndrezejewskietal.2017,
  author    = {Rudno-Rudziński, W. and Syperek, M. and Andrezejewski, J. and Maryński, A. and Misiewicz, J. and Somers, A. and H{\"o}fling, S. and Reithmaier, J. P. and Sęk, G.},
  title     = {Carrier delocalization in InAs/InGaAlAs/InP quantum-dash-based tunnel injection system for 1.55 μm emission},
  series = {AIP Advances},
  volume    = {7},
  journal   = {AIP Advances},
  number    = {1},
  doi       = {10.1063/1.4975634},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-181787},
  year      = {2017},
  abstract  = {We have investigated optical properties of hybrid two-dimensional-zero-dimensional (2D-0D) tunnel structures containing strongly elongated InAs/InP(001) quantum dots (called quantum dashes), emitting at 1.55 μm. These quantum dashes (QDashes) are separated by a 2.3 nm-width barrier from an InGaAs quantum well (QW), lattice matched to InP. We have tailored quantum-mechanical coupling between the states confined in QDashes and a QW by changing the QW thickness. By combining modulation spectroscopy and photoluminescence excitation, we have determined the energies of all relevant optical transitions in the system and proven the carrier transfer from the QW to the QDashes, which is the fundamental requirement for the tunnel injection scheme. A transformation between 0D and mixed-type 2D-0D character of an electron and a hole confinement in the ground state of the hybrid system have been probed by time-resolved photoluminescence that revealed considerable changes in PL decay time with the QW width changes. The experimental discoveries have been explained by band structure calculations in the framework of the eight-band k·p model showing that they are driven by delocalization of the lowest energy hole state. The hole delocalization process from the 0D QDash confinement is unfavorable for optical devices based on such tunnel injection structures.},
  language  = {en}
}
@phdthesis{Quast2017,
  author    = {Quast, Jan-Henrik},
  title     = {Influence of Hot Carriers on Spin Diffusion in Gallium Arsenide},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-147611},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {Since the late 20th century, spintroncis has become a very active field of research [ŽFS04]. The prospect of spin based information technology, featuring strongly decreased energy consumption and possibly quantum-computation capabilities, has fueled this interest. Standard materials, like bulk gallium arsenide (GaAs), have experienced new attention in this context by exhibiting extraordinarily long lifetimes for nonequilibrium spin information, which is an important requirement for efficient spin based information storage and transfer. Another important factor is the lengthscale over which spin information can be transported in a given material and the role of external influences. Both aspects have been studied experimentally with innovative optical methods since the late 1990s by the groups of D. D. AWSHALOM and S. A. CROOKER et al. [KA99, CS05, CFL+05]. Although the pioneering experimental approaches presented by these authors led to a variety of insights into spin propagation, some questions were raised as well. Most prominently, the classical Einstein relation, which connects the mobility and diffusivity of a given particle species, seemed to be violated for electron spins in a bulk semiconductor. In essence, nonequilibrium spins appeared to move (diffuse) faster than the electrons that actually carry the spin. However, this contradiction was masked by the fact, that the material of interest was n-type GaAs with a doping concentration directly at the transition between metallic and insulating behavior (MIT). In this regime, the electron mobility is difficult to determine experimentally. Consequently, it was not a priori obvious that the spin diffusion rates determined by the newly introduced optical methods were in contradiction with established electrical transport data. However, in an attempt to extend the available data of optical spin microscopy, another issue surfaced, concerning the mathematical drift-diffusion model that has been commonly used to evaluate lateral spin density measurements. Upon close investigation, this model appears to have a limited range of applicability, due to systematic discrepancies with the experimental data (chapter 4). These deviations are noticeable in original publications as well, and it is shown in the present work that they originate from the local heating of electrons in the process of optical spin pumping. Based on insights gained during the second half of the 20th century, it is recapitulated why conduction electrons are easily overheated at cryogenic temperatures. The main reason is the poor thermal coupling between electrons and the crystal lattice (chapter 3). Experiments in the present work showed that a significant thermal gradient exists in the conduction band under local optical excitation of electron-hole pairs. This information was used to develop a better mathematical model of spin diffusion, which allowed to derive the diffusivity of the undisturbed system, due to an effective consideration of electron overheating. In this way, spin diffusivities of n-GaAs were obtained as a function of temperature and doping density in the most interesting regime of the metal-insulator-transition. The experiments presented in this work were performed on a series of n-type bulk GaAs samples, which comprised the transition between metallic conductivity and electrical insulation at low temperatures. Local electron temperature gradients were measured by a hyperspectral photoluminescence imaging technique with subsequent evaluation of the electron-acceptor (e,A\$^0\$) line shape. The local density of nonequilibrium conduction electron spins was deduced from scanning magneto-optic Kerr effect microscopy. Numerical evaluations were performed using the finite elements method in combination with a least-squares fitting procedure. Chapter 1 provides an introduction to historical and recent research in the field of spintronics, as far as it is relevant for the understanding of the present work. Chapter 2 summarizes related physical concepts and experimental methods. Here, the main topics are semiconductor optics, relaxation of hot conduction electrons, and the dynamics of nonequilibrium electron spins in semiconductors. Chapter 3 discusses optical heating effects due to local laser excitation of electron-hole pairs. Experimental evaluations of the acceptor-bound-exciton triplet lines led to the conclusion that the crystal lattice is usually not overheated even at high excitation densities. Here, the heat is efficiently dissipated to the bath, due to the good thermal conductivity of the lattice. Furthermore, the heating of the lattice is inherently limited by the weak heat transfer from the electron system, which on the other hand is also the reason why conduction electrons are easily overheated at temperatures below ≈ 30 K. Spatio-spectral imaging of the electron-acceptor-luminescence line shape allowed to trace the thermal gradient within the conduction band under focused laser excitation. A heat-diffusion model was formulated, which reproduces the experimental electron-temperature trend nicely for low-doped GaAs samples of n- and p-type. For high-doped n-type GaAs samples, it could be shown that the lateral electron-temperature profile is well approximated by a Gaussian. This facilitated easy integration of hot electron influence into the mathematical model of spin diffusion. Chapter 4 deals with magneto-optical imaging of optically induced nonequilibrium conduction-electron spins in n-GaAs close to the MIT. First, the spectral dependence of the magneto-optic Kerr effect was examined in the vicinity of the fundamental band gap. Despite the marked differences among the investigated samples, the spectral shape of the Kerr rotation could be described in terms of a simple Lorentz-oscillator model in all cases. Based on this model, the linearity of the Kerr effect with respect to a nonequilibrium spin polarization is demonstrated, which is decisively important for further quantitative evaluations. Furthermore, chapter 4 presents an experimental survey of spin relaxation in n-GaAs at the MIT. Here, the dependence of the spin relaxation time on bath temperature and doping density was deduced from Hanle-MOKE measurements. While all observed trends agree with established literature, the presented results extend the current portfolio by adding a coherent set of data. Finally, diffusion of optically generated nonequilibrium conduction-electron spins was investigated by scanning MOKE microscopy. First, it is demonstrated that the standard diffusion model is inapplicable for data evaluation in certain situations. A systematic survey of the residual deviations between this model and the experimental data revealed that this situation unfortunately persisted in published works. Moreover, the temperature trend of the residual deviations suggests a close connection to the local overheating of conduction electrons. Consequently, a modified diffusion model was developed and evaluated, in order to compensate for the optical heating effect. From this model, much more reliable results were obtained, as compared to the standard diffusion model. Therefore, it was shown conclusively that the commonly reported anomalously large spin diffusivities were at least in parts caused by overheated conduction electrons. In addition to these new insights some experimental and technological enhancements were realized in the course of this work. First, the optical resolution of scanning MOKE microscopy was improved by implementing a novel scanning mechanism, which allows the application of a larger aperture objective than in the usual scheme. Secondly, imaging photoluminescence spectroscopy was employed for spatially resolved electron-temperature measurements. Here, two different implementations were developed: One for lattice-temperature measurements by acceptor-bound exciton luminescence and a second for conduction-electron temperature measurements via the analysis of the electron-acceptor luminescence line shape. It is shown in the present work that the originally stated anomalously high spin diffusivities were caused to a large extent by unwanted optical heating of the electron system. Although an efficient method was found to compensate for the influence of electron heating, it became also evident that the classical Einstein relation was nonetheless violated under the given experimental conditions. In this case however, it could be shown that this discrepancy did not originate from an experimental artifact, but was instead a manifestation of the fermionic nature of conduction electrons.},
  subject      = {Galliumarsenid},
  language  = {en}
}
@article{PollingerSchmittSanderetal.2017,
  author    = {Pollinger, Florian and Schmitt, Stefan and Sander, Dirk and Tian, Zhen and Kirschner, J{\"u}rgen and Vrdoljak, Pavo and Stadler, Christoph and Maier, Florian and Marchetto, Helder and Schmidt, Thomas and Sch{\"o}ll, Achim and Umbach, Eberhard},
  title     = {Nanoscale patterning, macroscopic reconstruction, and enhanced surface stress by organic adsorption on vicinal surfaces},
  series = {New Journal of Physics},
  volume    = {19},
  journal   = {New Journal of Physics},
  doi       = {10.1088/1367-2630/aa55b8},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-171947},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@phdthesis{Pakkayil2017,
  author    = {Pakkayil, Shijin Babu},
  title     = {Towards ferromagnet/superconductor junctions on graphene},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-153863},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {This thesis reports a successful fabrication and characterisation of ferromagnetic/superconductor junction (F/S) on graphene. The thesis preposes a fabrication method to produce F/S junctions on graphene which make use of ALD grown Al2O3 as the tunnel barrier for the ferromagnetic contacts. Measurements done on F/G/S/G/F suggests that by injecting spin polarised current into the superconductor, a spin imbalance is created in the quasiparticle density of states of the superconductor which then diffuses through the graphene channel. The observed characteristic curves are similar to the ones which are already reported on metallic ferromagnet/superconductor junctions where the spin imbalance is created using Zeeman splitting. Further measurements also show that the curves loose their characteristic shapes when the temperature is increased above the critical temperature (Tc) or when the external magnetic field is higher then the critical field (Hc) of the superconducting contact. But to prove conclusively and doubtlessly the existence of spin imbalance in ferromagnet/superconductor junctions on graphene, more devices have to be made and characterised preferably in a dilution refrigerator.},
  subject      = {Graphen},
  language  = {en}
}
@article{MinGothLutzetal.2017,
  author    = {Min, Chul-Hee and Goth, F. and Lutz, P. and Bentmann, H. and Kang, B.Y. and Cho, B.K. and Werner, J. and Chen, K.-S. and Assaad, F. and Reinert, F.},
  title     = {Matching DMFT calculations with photoemission spectra of heavy fermion insulators: universal properties of the near-gap spectra of SmB\(_{6}\)},
  series = {Scientific Reports},
  volume    = {7},
  journal   = {Scientific Reports},
  number    = {11980},
  doi       = {10.1038/s41598-017-12080-5},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-170328},
  year      = {2017},
  abstract  = {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\(_{6}\)).},
  language  = {en}
}
@phdthesis{Maier2017,
  author    = {Maier, Sebastian},
  title     = {Quantenpunktbasierte Einzelphotonenquellen und Licht-Materie-Schnittstellen},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-152972},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {Die Quanteninformationstechnologie ist ein Schwerpunkt intensiver weltweiter Forschungsarbeit, da sie L{\"o}sungen f{\"u}r aktuelle globale Probleme verspricht. So bietet die Quantenkommunikation (QKD, engl. quantum key distribution) absolut abh{\"o}rsichere Kommunikationsprotokolle und k{\"o}nnte, mit der Realisierung von Quantenrepeatern, auch {\"u}ber große Distanzen zum Einsatz kommen. Quantencomputer (engl. quantum computing) k{\"o}nnten von Nutzen sein, um sehr schwierige und komplexe mathematische Probleme schneller zu l{\"o}sen. Ein grundlegender kritischer Baustein der gesamten halbleiterbasierten Quanteninformationsverarbeitung (QIP, engl. quantum information processing) ist die Bereitstellung von Proben, die einerseits die geforderten physikalischen Eigenschaften aufweisen und andererseits den Anforderungen der komplexen Messtechnik gen{\"u}gen, um die Quanteneigenschaften nachzuweisen und technologisch nutzbar machen zu k{\"o}nnen. In halbleiterbasierten Ans{\"a}tzen haben sich Quantenpunkte als sehr vielversprechende Kandidaten f{\"u}r diese Experimente etabliert. Halbleiterquantenpunkte weisen große {\"A}hnlichkeiten zu einzelnen Atomen auf, die sich durch diskrete Energieniveaus und diskrete Spektrallinien im Emissionsspektrum manifestieren, und zeichnen sich {\"u}berdies als exzellente Emitter f{\"u}r einzelne und ununterscheidbare Photonen aus. Außerdem k{\"o}nnen mit Quantenpunkten zwei kritische Bausteine in der Quanteninformationstechnologie abgedeckt werden. So k{\"o}nnen station{\"a}re Quantenbits (Qubits) in Form von Elektronenspinzust{\"a}nden gespeichert werden und mittels Spin-Photon-Verschr{\"a}nkung weit entfernte station{\"a}re Qubits {\"u}ber fliegende photonische Qubits verschr{\"a}nkt werden. Die Herstellung und Charakterisierung von quantenpunktbasierten Halbleiterproben, die sich durch definierte Eigenschaften f{\"u}r Experimente in der QIP auszeichnen, steht im Mittelpunkt der vorliegenden Arbeit. Die Basis f{\"u}r das Probenwachstum bildet dabei das Materialsystem von selbstorganisierten In(Ga)As-Quantenpunkten auf GaAs-Substraten. Die Herstellung der Quantenpunktproben mittels Molekularstrahlepitaxie erm{\"o}glicht h{\"o}chste kristalline Qualit{\"a}ten und bietet die M{\"o}glichkeit, die Quantenemitter in photonische Resonatoren zu integrieren. Dadurch kann die Lichtauskoppeleffizienz stark erh{\"o}ht und die Emission durch Effekte der Licht-Materie-Wechselwirkung verst{\"a}rkt werden. Vor diesem Hintergrund wurden in der vorliegenden Arbeit verschiedene In(Ga)As-Quantenpunktproben mit definierten Anforderungen mittels Molekularstrahlepitaxie hergestellt und deren morphologische und optische Eigenschaften untersucht. F{\"u}r die Charakterisierung der Morphologie kamen Rasterelektronen- und Rasterkraftmikroskopie zum Einsatz. Die optischen Eigenschaften wurden mit Hilfe der Reflektions-, Photolumineszenz- und Resonanzfluoreszenz-Spektroskopie sowie Autokorrelationsmessungen zweiter Ordnung ermittelt. Der Experimentalteil der Arbeit ist in drei Kapitel unterteilt, deren Kerninhalte im Folgenden kurz wiedergegeben werden. Quasi-Planare Einzelphotonenquelle mit hoher Extraktionseffizienz: Planare quantenpunktbasierte Einzelphotonenquellen mit hoher Extraktionseffizienz sind f{\"u}r Experimente zur Spinmanipulation von herausragender Bedeutung. Elektronen- und Lochspins haben sich als gute Kandidaten erwiesen, um gezielt einzelne Elektronenspins zu initialisieren, manipulieren und zu messen. Ein einzelner Quantenpunkt muss einfach geladen sein, damit er im Voigt-Magnetfeld ein λ-System bilden kann, welches die grundlegende Konfiguration f{\"u}r Experimente dieser Art darstellt. Wichtig sind hier einerseits eine stabile Spinkonfiguration mit langer Koh{\"a}renzzeit und andererseits hohe Lichtauskoppeleffizienzen. Quantenpunkte in planaren Mikrokavit{\"a}ten weisen gr{\"o}ßere Werte f{\"u}r die Spindephasierungszeit auf als Mikro- und Nanot{\"u}rmchenresonatoren, dagegen ist bei planaren Proben die Lichtauskoppeleffizienz geringer. In diesem Kapitel wird eine quasi-planare quantenpunktbasierte Quelle f{\"u}r einzelne (g(2)(0)=0,023) und ununterscheidbare Photonen (g(2)indist (0)=0,17) mit hoher Reinheit vorgestellt. Die Quantenpunktemission weist eine sehr hohe Intensit{\"a}t und optische Qualit{\"a}t mit Halbwertsbreiten nahe der nat{\"u}rlichen Linienbreite auf. Die Auskoppeleffizienz wurde zu 42\% f{\"u}r reine Einzelphotonenemission bestimmt und {\"u}bersteigt damit die, f{\"u}r eine planare Resonatorstruktur erwartete, Extraktionseffizienz (33\%) deutlich. Als Grund hierf{\"u}r konnte die Kopplung der Photonenemission an Gallium-induzierte, Gauß-artige Defektstrukturen ausgemacht werden. Mithilfe morphologischer Untersuchungen und Simulationen wurde gezeigt, dass diese Defektkavit{\"a}ten einerseits als Nukleationszentren f{\"u}r das Quantenpunktwachstum dienen und andererseits die Extraktion des emittierten Lichts der darunterliegenden Quantenpunkte durch Lichtb{\"u}ndelung verbessern. In weiterf{\"u}hrenden Arbeiten konnte an dieser spezifischen Probe der fundamentale Effekt der Verschr{\"a}nkung von Elektronenspin und Photon nachgewiesen werden, der einen kritischen Baustein f{\"u}r halbleiterbasierte Quantenrepeater darstellt. Im Rahmen dieses Experiments war es m{\"o}glich, die komplette Tomographie eines verschr{\"a}nkten Spin-Photon-Paares an einer halbleiterbasierten Spin-Photon Schnittstelle zu messen. {\"U}berdies konnte Zweiphotoneninterferenz und Ununterscheidbarkeit von Photonen aus zwei r{\"a}umlich getrennten Quantenpunkten auf diesem Wafer gemessen werden, was ebenfalls einen kritischen Baustein f{\"u}r Quantenrepeater darstellt. Gekoppeltes Quantenfilm-Quantenpunkt System: Weitere Herausforderungen f{\"u}r optisch kontrollierte halbleiterbasierte Spin-Qubit-Systeme sind das schnelle und zerst{\"o}rungsfreie Auslesen der Spin-Information sowie die Implementierung eines skalierbaren Ein-Qubit- und Zwei-Qubit-Gatters. Ein k{\"u}rzlich ver{\"o}ffentlichtes theoretisches Konzept k{\"o}nnte hierzu einen eleganten Weg er{\"o}ffnen: Hierbei wird die spinabh{\"a}ngige Austauschwechselwirkung zwischen einem Elektron-Spin in einem Quantenpunkt und einem Exziton-Polariton-Gas, welches in einem nahegelegenen Quantenfilm eingebettet ist, ausgen{\"u}tzt. So k{\"o}nnte die Spin-Information zerst{\"o}rungsfrei ausgelesen werden und eine skalierbare Wechselwirkung zwischen zwei Qubits {\"u}ber gr{\"o}ßere Distanzen erm{\"o}glicht werden, da sich die Wellenfunktion von Exziton-Polaritonen, abh{\"a}ngig von der G{\"u}te des Mikroresonators, {\"u}ber mehrere μm ausdehnen kann. Dies und weitere m{\"o}gliche Anwendungen machen das gekoppelte Quantenfilm-Quantenpunkt System sehr interessant, weshalb eine grundlegende experimentelle Untersuchung dieses Systems w{\"u}nschenswert ist. In Zusammenarbeit mit der Arbeitsgruppe um Yoshihisa Yamamoto an der Universit{\"a}t Stanford, wurde hierzu ein konkretes Probendesign entwickelt und im Rahmen dieser Arbeit technologisch verwirklicht. Durch systematische epitaktische Optimierung ist es gelungen, ein gekoppeltes Quantenfilm-Quantenpunkt System erfolgreich in einen Mikroresonator zu implementierten. Das Exziton-Polariton-Gas konnte mittels eines Quantenfilms in starker Kopplung in einer Mikrokavit{\"a}t mit einer Rabi-Aufspaltung von VR=2,5 meV verwirklicht werden. Zudem konnten einfach geladene Quantenpunkte mit hoher optischer Qualit{\"a}t und klarem Einzelphotonencharakter (g(2)(0)=0,24) in unmittelbarer N{\"a}he zum Quantenfilm gemessen werden. Positionierte Quantenpunkte: F{\"u}r die Herstellung quantenpunktbasierter Einzelphotonenquellen mit hoher optischer Qualit{\"a}t ist eine skalierbare technologische Produktionsplattform w{\"u}nschenswert. Dazu m{\"u}ssen einzelne Quantenpunkte positionierbar und somit deterministisch und skalierbar in Bauteile integriert werden k{\"o}nnen. Basierend auf zweidimensionalen, regelm{\"a}ßig angeordneten und dadurch adressierbaren Quantenpunkten gibt es zudem ein Konzept, um ein skalierbares, optisch kontrolliertes Zwei-Qubit-Gatter zu realisieren. Das hier verfolgte Prinzip f{\"u}r die Positionierung von Quantenpunkten beruht auf der Verwendung von vorstrukturierten Substraten mit ge{\"a}tzten Nanol{\"o}chern, welche als Nukleationszentren f{\"u}r das Quantenpunktwachstum dienen. Durch eine optimierte Schichtstruktur und eine erh{\"o}hte Lichtauskopplung unter Verwendung eines dielektrischen Spiegels konnte erstmals Resonanzfluoreszenz an einem positionierten Quantenpunkt gemessen werden. In einem weiteren Optimierungsansatz konnte außerdem Emission von positionierten InGaAs Quantenpunkten auf GaAs Substrat bei 1,3 μm Telekommunikationswellenl{\"a}nge erreicht werden.},
  subject      = {Quantenpunkt},
  language  = {de}
}
@phdthesis{Maass2017,
  author    = {Maaß, Henriette},
  title     = {Spin-dependence of angle-resolved photoemission from spin-orbit split surface states},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-151025},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {Spin- and angle-resolved photoelectron spectroscopy is the prime method to investigate spin polarized electronic states at solid state surfaces. In how far the spin polarization of an emitted photoelectron reflects the intrinsic spin character of an electronic state is the main question in the work at hand. It turns out that the measured spin polarization is strongly influenced by experimental conditions, namely by the polarization of the incoming radiation and the excitation energy. The photoemission process thus plays a non-negligible role in a spin-sensitive measurement. This work is dedicated to unravel the relation between the result of a spin-resolved measurement and the spin character in the ground state and, therefore, to gain a deep understanding of the spin-dependent photoemission process. Materials that exhibit significant spin-splittings in their electronic structure, owing to a strong spin-orbit coupling, serve as model systems for the investigations in this work. Therefore, systems with large Rashba-type spin-splittings as BiTeI(0001) and the surface alloys BiAg2/Ag(111) and PbAg2/Ag(111) are investigated. Likewise, the surface electronic structure of the topological insulators Bi2Te2Se(0001) and Bi2Te3(0001) are analyzed. Light polarization dependent photoemission experiments serve as a probe of the orbital composition of electronic states. The knowledge of the orbital structure helps to disentangle the spin-orbital texture inherent to the different surface states, when in addition the spin-polarization is probed. It turns out that the topological surface state of Bi2Te2Se(0001) as well as the Rashba-type surface state of BiTeI(0001) exhibit chiral spin-textures associated with the p-like in-plane orbitals. In particular, opposite chiralities are coupled to either tangentially or radially aligned p-like orbitals, respectively. The results presented here are thus evidence that a coupling between spin- and orbital part of the wave function occurs under the influence of spin-orbit coupling, independent of the materials topology. Systematic photon energy dependent measurements of the out-of-plane spin polarization of the topological surface state of Bi2Te3(0001) reveal a strong dependence and even a reversal of the sign of the photoelectron spin polarization with photon energy. Similarly, the measured spin component perpendicular to the wave vector of the surface state of BiAg2/Ag(111) shows strong modulations and sign reversals when the photon energy is changed. In BiAg2/Ag(111) the variations in the photoelectron spin polarization are accompanied by significant changes and even a complete suppression of the photoemission intensity from the surface state, indicating that the variations of the spin polarization are strongly related to the photoemission cross section. This relation is finally analyzed in detail by employing a simple model, which is based on an evaluation of the transition matrix elements that describe the presented experiments. The model shows that the underlying cause for the observed photoelectron spin reversals can be found in the coupling of the spin structure to the spatial part of the initial state wave function, revealing the crucial role of spin-orbit interaction in the initial state wave function. The model is supported by ab initio photoemission calculations, which show strong agreement with the experimental results.},
  subject      = {Photoelektronenspektroskopie},
  language  = {en}
}
@phdthesis{Leubner2017,
  author    = {Leubner, Philipp},
  title     = {Strain-engineering of the Topological Insulator HgTe},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-152446},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {The subject of this thesis is the control of strain in HgTe thin-film crystals. Such systems are members of the new class of topological insulator materials and therefore of special research interest. A major task was the experimental control of the strain in the HgTe films. This was achieved by a new epitaxial approach and confirmed by cristallographic analysis and magneto-transport measurements. In this work, strain was induced in thin films by means of coherent epitaxy on substrate crystals. This means that the film adopts the lattice constant of the substrate in the plane of the substrate-epilayer interface. The level of strain is determined by the difference between the strain-free lattice constants of the substrate and epilayer material (the so-called lattice mismatch). The film responds to an in-plane strain with a change of its lattice constant perpendicular to the interface. This relationship is crucial for both the correct interpretation of high resolution X-ray diffraction (HRXRD) measurements, and the precise determination of the band dispersion. The lattice constant of HgTe is smaller than the lattice constant of CdTe. Therefore, strain in HgTe is tensile if it is grown on a CdTe substrate. In principle, compressive strain can be achieved by using an appropriate \(\text{Cd}_{1-x}\text{Zn}_{x}\text{Te}\) substrate. This concept was modified and applied in this work. Epilayers have been fabricated by molecular-beam epitaxy (MBE). The growth of thick buffer layers of CdTe on GaAs:Si was established as an alternative to commercial CdTe and \(text{Cd}_{0.96}\text{Zn}_{0.04}\text{Te}\) substrates. The growth conditions have been optimized by an analysis of atomic force microscopy and HRXRD studies. HRXRD measurements reveal a power-law increase of the crystal quality with increasing thickness. Residual strain was found in the buffer layers, and was attributed to a combination of finite layer thickness and mismatch of the thermal expansion coefficients of CdTe and GaAs. In order to control the strain in HgTe epilayers, we have developed a new type of substrate with freely adjustable lattice constant. CdTe-\(\text{Cd}_{0.5}\text{Zn}_{0.5}\text{Te}\) strained-layer-superlattices have been grown by a combination of MBE and atomic-layer epitaxy (ALE), and have been analyzed by HRXRD. ALE of the \(\text{Cd}_{0.5}\text{Zn}_{0.5}\text{Te}\) layer is self-limiting to one monolayer, and the effective lattice constant can be controlled reproducibly and straightforward by adjusting the CdTe layer thickness. The crystal quality has been found to degrade with increasing Zn-fraction. However, the effect is less drastic compared to single layer \(\text{Cd}_{1-x}\text{Zn}_{x}\text{Te}\) solid solutions. HgTe quantum wells (QWs) sandwiched in between CdHgTe barriers have been fabricated in a similar fashion on superlattices and conventional CdTe and \(\text{Cd}_{0.96}\text{Zn}_{0.04}\text{Te}\) substrates. The lower critical thickness of the CdHgTe barrier material grown on superlattice substrates had to be considered regarding the sample design. The electronic properties of the QWs depend on the strain and thickness of the QW. We have determined the QW thickness with an accuracy of \(\pm\)0.5 nm by an analysis of the beating patterns in the thickness fringes of HRXRD measurements and X-ray reflectometry measurements. We have, for the first time, induced compressive strain in HgTe QWs by an epitaxial technique (i.e. the effective lattice constant of the superlattice is lower compared to the lattice constant of HgTe). The problem of the lattice mismatch between superlattice and barriers has been circumvented by using CdHgTe-ZnHgTe superlattices instead of CdHgTe as a barrier material. Furthermore, the growth of compressively strained HgTe bulk layers (with a thickness of at least 50 nm) was demonstrated as well. The control of the state of strain adds a new degree of freedom to the design of HgTe epilayers, which has a major influence on the band structure of QWs and bulk layers. Strain in bulk layers lifts the degeneracy of the \(\Gamma_8\) bands at \(\mathbf{k}=0\). Tensile strain opens an energy gap, compressive strain shifts the touching points of the valence- and conduction band to positions in the Brillouin zone with finite \(\mathbf{k}\). Such a situation has been realized for the first time in the course of this work. For QWs in the inverted regime, it is demonstrated that compressive strain can be used to significantly enhance the thermal energy gap of the two-dimensional electron gas (2DEG). In addition, semi-metallic and semiconducting behavior is expected in wide QWs, depending on the state of strain. An examination of the temperature dependence of the subband ordering in QWs revealed that the band gap is only temperature-stable for appropriate sample parameters and temperature regimes. The band inversion is always lifted for sufficiently high temperatures. A large number of models investigate the influence of the band gap on the stability of the quantum-spin-Hall (QSH) effect. An enhancement of the stability of QSH edge state conductance is expected for enlarged band gaps. Furthermore, experimental studies on the temperature dependence of the QSH conductance are in contradiction to theoretical predictions. Systematic studies of these aspects have become feasible based on the new flexibility of the sample design. Detailed low-temperature magnetotransport studies have been carried out on QWs and bulk layers. For this purpose, devices have been fabricated lithographically, which consist of two Hall-bar geometries with different dimensions. This allows to discriminate between conductance at the plane of the 2DEG and the edge of the sample. The Fermi energy in the 2DEG has been adjusted by means of a top gate electrode. The strain-induced transition from semi-metallic to semiconducting characteristics in wide QWs was shown. The magnitude of the semi-metallic overlap of valence- and conduction band was determined by an analysis of the two-carrier conductance and is in agreement with band structure calculations. The band gap of the semiconducting sample was determined by measurements of the temperature dependence of the conductance at the charge-neutrality point. Agreement with the value expected from theory has been achieved for the first time in this work. The influence of the band gap on the stability of QSH edge state conductance has been investigated on a set of six samples. The band gap of the set spans a range of 10 to 55 meV. The latter value has been achieved in a highly compressively strained QW, has been confirmed by temperature-dependent conductance measurements, and is the highest ever reported in the inverted regime. Studies of the carrier mobility reveal a degradation of the sample quality with increasing Zn-fraction in the superlattice, in agreement with HRXRD observations. The enhanced band gap does not suppress scattering mechanisms in QSH edge channels, but lowers the conductance in the plane of the 2DEG. Hence, edge state conductance is the dominant conducting process even at elevated temperatures. An increase in conductance with increasing temperature has been found, in agreement with reports from other groups. The increase follows a power-law dependency, the underlying physical mechanism remains open. A cause for the lack of an increase of the QSH edge state conductance with increasing energy gap has been discussed. Possibly, the sample remains insulating even at finite carrier densities, due to localization effects. The measurement does not probe the QSH edge state conductance at the situation where the Fermi energy is located in the center of the energy gap, but in the regime of maximized puddle-driven scattering. In a first set of measurements, it has been shown that the QSH edge state conductance can be influenced by hysteretic charging effects of trapped states in the insulating dielectric. A maximized conductance of \(1.6\ \text{e}^2/\text{h}\) was obtained in a \(58\ \mu\text{m}\) edge channel. Finally, measurements on three dimensional samples have been discussed. Recent theoretical works assign compressively strained HgTe bulk layers to the Weyl semi-metal class of materials. Such layers have been synthesized and studied in magnetotransport experiments for the first time. Pronounced quantum-Hall- and Shubnikov-de-Haas features in the Hall- and longitudinal resistance indicate two-dimensional conductance on the sample surface. However, this conductance cannot be assigned definitely to Weyl surface states, due to the inversion of \(\Gamma_6\) and \(\Gamma_8\) bands. If a magnetic field is aligned parallel to the current in the device, a decrease in the longitudinal resistance is observed with increasing magnetic field. This is a signature of the chiral anomaly, which is expected in Weyl semi-metals.},
  subject      = {Quecksilbertellurid},
  language  = {en}
}
@phdthesis{Kuger2017,
  author    = {Kuger, Fabian},
  title     = {Signal Formation Processes in Micromegas Detectors and Quality Control for large size Detector Construction for the ATLAS New Small Wheel},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-152495},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {The Micromegas technology is one of the most successful modern gaseous detector concepts and widely utilized in nuclear and particle physics experiments. Twenty years of R \& D rendered the technology sufficiently mature to be selected as precision tracking detector for the New Small Wheel (NSW) upgrade of the ATLAS Muon spectrometer. This will be the first large scale application of Micromegas in one of the major LHC experiments. However, many of the fundamental microscopic processes in these gaseous detectors are still not fully understood and studies on several detector aspects, like the micromesh geometry, have never been addressed systematically. The studies on signal formation in Micromegas, presented in the first part of this thesis, focuses on the microscopic signal electron loss mechanisms and the amplification processes in electron gas interaction. Based on a detailed model of detector parameter dependencies, these processes are scrutinized in an iterating comparison between exper- imental results, theory prediction of the macroscopic observables and process simulation on the microscopic level. Utilizing the specialized detectors developed in the scope of this thesis as well as refined simulation algorithms, an unprecedented level of accuracy in the description of the microscopic processes is reached, deepening the understanding of the fundamental process in gaseous detectors. The second part is dedicated to the challenges arising with the large scale Micro- megas production for the ATLAS NSW. A selection of technological choices, partially influenced or determined by the herein presented studies, are discussed alongside a final report on two production related tasks addressing the detectors' core components: For the industrial production of resistive anode PCBs a detailed quality control (QC) and quality assurance (QA) scheme as well as the therefore required testing tools have been developed. In parallel the study on micromesh parameter optimization and production feasibility resulted in the selection of the proposed mesh by the NSW community and its full scale industrial manufacturing. The successful completion of both tasks were im- portant milestones towards the construction of large size Micromegas detectors clearing the path for NSW series production.},
  subject      = {Gasionisationsdetektor},
  language  = {en}
}
@article{KaireitSorrentinoRenneetal.2017,
  author    = {Kaireit, Till F. and Sorrentino, Sajoscha A. and Renne, Julius and Schoenfeld, Christian and Voskrebenzev, Andreas and Gutberlet, Marcel and Schulz, Angela and Jakob, Peter M. and Hansen, Gesine and Wacker, Frank and Welte, Tobias and T{\"u}mmler, Burkhard and Vogel-Claussen, Jens},
  title     = {Functional lung MRI for regional monitoring of patients with cystic fibrosis},
  series = {PLoS ONE},
  volume    = {12},
  journal   = {PLoS ONE},
  number    = {12},
  doi       = {10.1371/journal.pone.0187483},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172457},
  year      = {2017},
  abstract  = {Purpose To test quantitative functional lung MRI techniques in young adults with cystic fibrosis (CF) compared to healthy volunteers and to monitor immediate treatment effects of a single inhalation of hypertonic saline in comparison to clinical routine pulmonary function tests. Materials and methods Sixteen clinically stable CF patients and 12 healthy volunteers prospectively underwent two functional lung MRI scans and pulmonary function tests before and 2h after a single treatment of inhaled hypertonic saline or without any treatment. MRI-derived oxygen enhanced T1 relaxation measurements, fractional ventilation, first-pass perfusion parameters and a morpho-functional CF-MRI score were acquired. Results Compared to healthy controls functional lung MRI detected and quantified significantly increased ventilation heterogeneity in CF patients. Regional functional lung MRI measures of ventilation and perfusion as well as the CF-MRI score and pulmonary function tests could not detect a significant treatment effect two hours after a single treatment with hypertonic saline in young adults with CF (p>0.05). Conclusion This study shows the feasibility of functional lung MRI as a non-invasive, radiation-free tool for monitoring patients with CF.},
  language  = {en}
}
@phdthesis{Huewe2017,
  author    = {H{\"u}we, Florian},
  title     = {Electrothermal Investigation on Charge and Heat Transport in the Low-Dimensional Organic Conductor (DCNQI)\(_2\)Cu},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-153492},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {This thesis aimed at the coherent investigation of the electrical and thermal transport properties of the low-dimensional organic conductor (DCNQI)2M (DCNQI: dicyanoquinonediimine; M: metallic counterion). These radical anion salts present a promising, new material class for thermoelectric applications and hence, a consistent characterization of the key parameters is required to evaluate and to optimize their performance. For this purpose, a novel experimental measurement setup enabling the determination of the electrical conductivity, the Seebeck coefficient and the thermal conductivity on a single crystalline specimen has been designed and implemented in this work. The novel measurement setup brought to operation within this thesis enabled a thorough investigation of the thermal transport properties in the (DCNQI)2M system. The thermal conductivity of (DCNQI-h8)2Cu at RT was determined to κ=1.73 W m^(-1) K^(-1). By reducing of the copper content in isostructural, crystalline (DMe-DCNQI)2CuxLi1-x alloys, the electrical conductivity has been lowered by one order of magnitude and the correlated changes in the thermal conductivity allowed for a verification of the Wiedemann-Franz (WF) law at RT. A room temperature Lorenz number of L=(2.48±0.45)⋅〖10〗^(-8) WΩK^(-2) was obtained in agreement with the standard Lorenz number L_0=2,44⋅〖10〗^(-8) WΩK^(-2) for 3D bulk metals. This value appears to be significantly reduced upon cooling below RT, even far above the Debye temperature of θ_D≈82 K, below which a breakdown of the WF law is caused by different relaxation times in response to thermal and to electric field perturbations. The experimental data enabled the first consistent evaluation of the thermoelectric performance of (DCNQI)\$_2\$Cu. The RT power factor of 110 μWm^(-1) K^(-2) is comparable to values obtained on PEDOT-based thermoelectric polymers. The RT figure of merit amounts to zT=0.02 which falls short by a factor of ten compared to the best values of zT=0.42 claimed for conducting polymers. It originates from the larger thermal conductivity in the organic crystals of about 1.73 W m^(-1) K^(-1) in (DCNQI)2Cu. Yet, more elaborate studies on the anisotropy of the thermal conductivity in PEDOT polymers assume their figure of merit to be zT=0.15 at most, recently. Therefore, (DCNQI)2Cu can be regarded as thermoelectric material of similar performance to polymer-based ones. Moreover, it represents one of the best organic n-type thermoelectric materials to date and as such, may also become important in hybrid thermoelectrics in combination with conducting polymers. Upon cooling below room temperature, (DCNQI)2Cu reveals its full potential attaining power factors of 50 mW K^(-2) m^(-1) and exceeding values of zT>0.15 below 40 K. These values represent the best thermoelectric performance in this low-temperature regime for organic as well as inorganic compounds and thus, low-dimensional organic conductors might pave the way toward new applications in cryogenic thermoelectrics. Further improvements may be expected from optimizing the charge carrier concentration by taking control over the CT process via the counterion stack of the crystal lattice. The concept has also been demonstrated in this work. Moreover, the thermoelectric performance in the vicinity of the CDW transition in (MeBr-DCNQI)2Cu was found to be increased by a factor of 5. Accordingly, the diversity of electronic ground states accessible in organic conductors provides scope for further improvements. Finally, the prototype of an all-organic thermoelectric generator has been built in combination with the p-type organic metal TTT2I3. While it only converts about 0.02\% of the provided heat into electrical energy, the specific power output per active area attains values of up to 5 mW cm^(-2). This power output, defining the cost-limiting factor in the recovery of waste heat, is three orders of magnitude larger than in conducting polymer devices and as such, unrivaled in organic thermoelectrics. While the thermoelectric key parameters of (DCNQI)2Cu still lack behind conventional thermoelectrics made of e.g. Bi2Te3, the promising performance together with its potential for improvements make this novel material class an interesting candidate for further exploration. Particularly, the low-cost and energy-efficient synthesis routes of organic materials highlight their relevance for technological applications.},
  subject      = {Radikalanionensalz},
  language  = {en}
}
@article{HeroldHerzWinteretal.2017,
  author    = {Herold, Volker and Herz, Stefan and Winter, Patrick and Gutjahr, Fabian Tobias and Andelovic, Kristina and Bauer, Wolfgang Rudolf and Jakob, Peter Michael},
  title     = {Assessment of local pulse wave velocity distribution in mice using k-t BLAST PC-CMR with semi-automatic area segmentation.},
  series = {Journal of Cardiovascular Magnetic Resonance},
  volume    = {19},
  journal   = {Journal of Cardiovascular Magnetic Resonance},
  number    = {77},
  doi       = {10.1186/s12968-017-0382-2},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-157696},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@phdthesis{Hansen2017,
  author    = {Hansen, Nis Hauke},
  title     = {Mikroskopische Ladungstransportmechanismen und Exzitonen Annihilation in organischen Einkristallen und D{\"u}nnschichten},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-143972},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {Um die Natur der Transportdynamik von Ladungstr{\"a}gern auch auf mikroskopischen L{\"a}ngenskalen nicht-invasiv untersuchen zu k{\"o}nnen, wurde im ersten Schwerpunkt dieser Arbeit das PL- (Photolumineszenz-) Quenching (engl.: to quench: l{\"o}schen; hier: strahlungslose Rekombination von Exzitonen) in einer organischen D{\"u}nnschicht durch die injizierten und akkumulierten L{\"o}cher in einer Transistorgeometrie analysiert. Diese Zusammenf{\"u}hrung zweier Methoden - der elektrischen Charakterisierung von D{\"u}nnschichttransistoren und der Photolumineszenzspektroskopie - erfasst die {\"A}nderung des strahlenden Zerfalls von Exzitonen infolge der Wechselwirkung mit Ladungstr{\"a}gern. Dadurch werden r{\"a}umlich aufgel{\"o}ste Informationen {\"u}ber die Ladungsverteilung und deren Spannungsabh{\"a}ngigkeit im Transistorkanal zug{\"a}nglich. Durch den Vergleich mit den makroskopischen elektrischen Kenngr{\"o}ßen wie der Schwell- oder der Turn-On-Spannung kann die Funktionsweise der Transistoren damit detaillierter beschrieben werden, als es die Kenngr{\"o}ßen alleine erm{\"o}glichen. Außerdem wird die Quantifizierung dieser mikroskopischen Interaktionen m{\"o}glich, welche beispielsweise als Verlustkanal in organischen Photovoltaikzellen und organicshen Leuchtdioden auftreten k{\"o}nnen. Die Abgrenzung zu anderen dissipativen Prozessen, wie beispielsweise der Exziton-Exziton Annihilation, Ladungstr{\"a}gerrekombination, Triplett-{\"U}berg{\"a}nge oder Rekombination an St{\"o}rstellen oder metallischen Grenzfl{\"a}chen, erlaubt die detaillierte Analyse der Wechselwirkung von optisch angeregten Zust{\"a}nden mit Elektronen und L{\"o}chern. Im zweiten Schwerpunkt dieser Arbeit werden die Transporteigenschaften des Naphthalindiimids Cl2-NDI betrachtet, bei dem der molekulare {\"U}berlapp sowie die Reorganisationsenergie in derselben Gr{\"o}ßenordnung von etwa 0,1 eV liegen. Um experimentell auf den mikroskopischen Transport zu schließen, werden nach der Optimierung des Kristallwachstums Einkristalltransistoren hergestellt, mit Hilfe derer die Beweglichkeit entlang verschiedener kristallographischer Richtungen als Funktion der Temperatur gemessen werden kann. Die einkristalline Natur der Proben und die spezielle Transistorgeometrie erm{\"o}glichen die Analyse der r{\"a}umlichen Anisotropie des Stromflusses. Der gemessene Beweglichkeitstensor wird daraufhin mit simulierten Tensoren auf der Basis von Levich-Jortner Raten verglichen, um auf den zentralen Ladungstransfermechanismus zu schließen.},
  subject      = {Organischer Halbleiter},
  language  = {de}
}
@article{GotschyBauerWinteretal.2017,
  author    = {Gotschy, Alexander and Bauer, Wolfgang R. and Winter, Patrick and Nordbeck, Peter and Rommel, Eberhard and Jakob, Peter M. and Herold, Volker},
  title     = {Local versus global aortic pulse wave velocity in early atherosclerosis: An animal study in ApoE\(^{-/-}\) mice using ultrahigh field MRI},
  series = {PLoS ONE},
  volume    = {12},
  journal   = {PLoS ONE},
  number    = {2},
  doi       = {10.1371/journal.pone.0171603},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-171824},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@phdthesis{Feichtner2017,
  author    = {Feichtner, Thorsten},
  title     = {Optimal Design of Focusing Nanoantennas for Light : Novel Approaches: From Evolution to Mode-Matching},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-140604},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {Optische Antennen arbeiten {\"a}hnlich wie Antennen f{\"u}r Radiowellen und wandeln elektromagnetische Strahlung in elektrische Wechselstr{\"o}me um. Ladungsdichteansammlungen an der Antennen-Oberfl{\"a}che f{\"u}hren zu starken und lokalisierten Nahfeldern. Da die meisten optischen Antennen eine Ausdehnung von wenigen hundert Nanometern besitzen, erm{\"o}glichen es ihre Nahfelder, Licht auf ein Volumen weit unterhalb des Beugungslimits zu fokussieren, mit Intensit{\"a}ten, die mehrere Gr{\"o}ßenordnungen {\"u}ber dem liegen, was man mit klassischer beugender und reflektierender Optik erreichen kann. Die Aufgabe, die Abstrahlung eines Quantenemitters zu maximieren, eines punktf{\"o}rmigen Objektes, welches einzelne Photonen absorbieren und emittieren kann, ist identisch mit der Aufgabe, die Feldintensit{\"a}t am Ort des Quantenemitters zu maximieren. Darum ist es erstrebenswert, den Fokus optischer Antennen zu optimieren Optimierte Radiofrequenz-Antennen, welche auf Gr{\"o}ßenordnungen von wenigen 100 Nanometern herunterskaliert werden, zeigen bereits eine gute Funktionalit{\"a}t. Jedoch liegen optische Frequenzen in der N{\"a}he der Plasmafrequenz von den Metallen, die f{\"u}r optische Antennen genutzt werden und die Masse der Elektronen kann nicht mehr vernachl{\"a}ssigt werden. Dadurch treten neue physikalische Ph{\"a}nomene auf. Es entstehen gekoppelte Zust{\"a}nde aus Licht und Ladungsdichte-Schwingungen, die sogenannten Plasmonen. Daraus folgen Effekte wie Volumenstr{\"o}me und k{\"u}rzere effektive Wellenl{\"a}ngen. Zus{\"a}tzlich f{\"u}hrt die endliche Leitf{\"a}higkeit zu thermischen Verluste. Das macht eine Antwort auf die Frage nach der optimalen Geometrie f{\"u}r fokussierende optische Antennen schwer. Jedoch stand vor dieser Arbeit der Beweis noch aus, dass es f{\"u}r optische Antennen bessere Alternativen gibt als herunterskalierte Radiofrequenz-Konzepte. In dieser Arbeit werden optische Antennen auf eine bestm{\"o}gliche Fokussierung optimiert. Daf{\"u}r wird ein Ansatz gew{\"a}hlt, welcher bei Radiofrequenz-Antennen f{\"u}r komplexe Anwendungsfelder (z.B. isotroper Breitbandempfang) schon oft Erfolg hatte: evolution{\"a}re Algorithmen. Die hier eingef{\"u}hrte erste Implementierung erlaubt eine große Freiheit in Bezug auf Partikelform und Anzahl, da sie quadratische Voxel auf einem planaren, quadratischen Gitter beliebig anordnet. Die Geometrien werden in einer bin{\"a}ren Matrix codiert, welche als Genom dient und somit Methoden wie Mutation und Paarung als Verbesserungsmechanismus erlaubt. So optimierte Antennen-Geometrien {\"u}bertreffen vergleichbare klassische Dipol-Geometrien um einen Faktor von Zwei. Dar{\"u}ber hinaus l{\"a}sst sich aus den optimierten Antennen ein neues Funktionsprinzip ableiten: ein magnetische Split-Ring-Resonanz kann mit Dipol-Antennen leitend zu neuartigen und effektiveren Split-Ring-Antennen verbunden werden, da sich ihre Str{\"o}me nahe des Fokus konstruktiv {\"u}berlagern. Im n{\"a}chsten Schritt wird der evolution{\"a}re Algorithmus so angepasst, so die Genome real herstellbare Geometrien beschreiben. Zus{\"a}tzlich wird er um eine Art ''Druckertreiber'' erweitert, welcher aus den Genomen direkt Anweisungen zur fokussierten Ionenstrahl-Bearbeitung von einkristallinen Goldflocken erstellt. Mit Hilfe von konfokaler Mikroskopie der Zwei-Photonen-Photolumineszenz wird gezeigt, dass Antennen unterschiedlicher Effizienz reproduzierbar aus dem evolution{\"a}ren Algorithmus heraus hergestellt werden k{\"o}nnen. Außerdem wird das Prinzip der Split-Ring-Antenne verbessert, indem zwei Ring-Resonanzen zu einer Dipol-Resonanz hinzugef{\"u}gt werden. Zu guter Letzt dient die beste Antenne des zweiten evolution{\"a}re Algorithmus als Inspiration f{\"u}r einen neuen Formalismus zur Beschreibung des Leistungs{\"u}bertrages zwischen einer optischen Antenne und einem Punkt-Dipol, welcher sich als "dreidimensionaler Moden{\"u}berlapp" beschreiben l{\"a}sst. Damit k{\"o}nnen erstmals intuitive Regeln f{\"u}r die Form einer optischen Antenne aufgestellt werden. Die G{\"u}ltigkeit der Theorie wird analytisch f{\"u}r den Fall eines Dipols nahe einer metallischen Nano-Kugel gezeigt. Das vollst{\"a}ndige Problem, Licht mittels einer optischen Antenne zu fokussieren, l{\"a}sst sich so auf die Erf{\"u}llung zweier Moden{\"u}berlapp-Bedingungen reduzieren -- mit dem Feld eines Punktdipols, sowie mit einer ebenen Welle. Damit lassen sich zwei Arten idealer Antennenmoden identifizieren, welche sich von der bekannten Dipol-Antennen-Mode grundlegend unterscheiden. Zum einen l{\"a}sst sich dadurch die Funktionalit{\"a}t der evolution{\"a}ren und Split-Ring-Antennen erkl{\"a}ren, zum lassen sich neuartige plasmonische Hohlraum-Antennen entwerfen, welche zu besserer Fokussierung von Licht f{\"u}hren. Dies wird numerisch im direkten Vergleich mit einer klassischen Dipolantennen-Geometrie gezeigt.},
  subject      = {Physik},
  language  = {en}
}
@article{ElsaesserSchieblMukhinetal.2017,
  author    = {Els{\"a}sser, S. and Schiebl, M. and Mukhin, A. A. and Balbashov, A. M. and Pimenov, A. and Geurts, J.},
  title     = {Impact of temperature-dependent local and global spin order in \(R\)MnO\(_3\) compounds for spin-phonon coupling and electromagnon activity},
  series = {New Journal of Physics},
  volume    = {19},
  journal   = {New Journal of Physics},
  doi       = {10.1088/1367-2630/aa55ed},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-171978},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@article{DziomShuvaevPimenovetal.2017,
  author    = {Dziom, V. and Shuvaev, A. and Pimenov, A. and Astakhov, G.V. and Ames, C. and Bendias, K. and B{\"o}ttcher, J. and Tkachov, G. and Hankiewicz, E.M. and Br{\"u}ne, C. and Buhmann, H. and Molenkamp, L.W.},
  title     = {Observation of the universal magnetoelectric effect in a 3D topological insulator},
  series = {Nature Communications},
  volume    = {8},
  journal   = {Nature Communications},
  number    = {15197},
  doi       = {10.1038/ncomms15197},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-170875},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@article{DeaconWiedenmannBocquillonetal.2017,
  author    = {Deacon, R. S. and Wiedenmann, J. and Bocquillon, E. and Dom{\´i}nguez, F. and Klapwijk, T. M. and Leubner, P. and Br{\"u}ne, C. and Hankiewicz, E. M. and Tarucha, S. and Ishibashi, K. and Buhmann, H. and Molenkamp, L. W.},
  title     = {Josephson Radiation from Gapless Andreev Bound States in HgTe-Based Topological Junctions},
  series = {Physical Review X},
  volume    = {7},
  journal   = {Physical Review X},
  number    = {021011},
  doi       = {10.1103/PhysRevX.7.021011},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-170969},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@phdthesis{Carinci2017,
  author    = {Carinci, Flavio},
  title     = {Quantitative Characterization of Lung Tissue Using Proton MRI},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-151189},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {The focus of the work concerned the development of a series of MRI techniques that were specifically designed and optimized to obtain quantitative and spatially resolved information about characteristic parameters of the lung. Three image acquisition techniques were developed. Each of them allows to quantify a different parameter of relevant diagnostic interest for the lung, as further described below: 1) The blood volume fraction, which represents the amount of lung water in the intravascular compartment expressed as a fraction of the total lung water. This parameter is related to lung perfusion. 2) The magnetization relaxation time T\(_2\) und T� *\(_2\) , which represents the component of T\(_2\) associated with the diffusion of water molecules through the internal magnetic field gradients of the lung. Because the amplitude of these internal gradients is related to the alveolar size, T\(_2\) und T� *\(_2\) can be used to obtain information about the microstructure of the lung. 3) The broadening of the NMR spectral line of the lung. This parameter depends on lung inflation and on the concentration of oxygen in the alveoli. For this reason, the spectral line broadening can be regarded as a fingerprint for lung inflation; furthermore, in combination with oxygen enhancement, it provides a measure for lung ventilation.},
  subject      = {Kernspintomografie},
  language  = {en}
}
@article{BiedermannBraeuerDenneretal.2017,
  author    = {Biedermann, Benedikt and Br{\"a}uer, Stephan and Denner, Ansgar and Pellen, Mathieu and Schumann, Steffen and Thompson, Jennifer M.},
  title     = {Automation of NLO QCD and EW corrections with SHERPA and RECOLA},
  series = {European Physical Journal C},
  volume    = {77},
  journal   = {European Physical Journal C},
  number    = {492},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-170615},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@phdthesis{Benkert2017,
  author    = {Benkert, Andreas},
  title     = {Soft x-ray spectroscopic study of methanol and glycine peptides in different physical environments},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-147111},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {Ionenspezifische Effekte treten in einer Vielzahl von w{\"a}ssrigen L{\"o}sungen aus Elektrolyten und gr{\"o}ßeren Molek{\"u}len wie Peptiden auf. Die Ionen bewirken dabei {\"A}nderungen in Eigenschaften wie z.B. der Viskosit{\"a}t, den Aktivit{\"a}ten von Enzymen, der Stabilit{\"a}t von Proteinen und deren Ein- bzw. Aussalzverhalten. Typischerweise wird die ionenabh{\"a}ngige Auspr{\"a}gung derartiger Effekte mithilfe der Hofmeister-Serie beschrieben, die urspr{\"u}nglich Ionen nach ihrer F{\"a}higkeit ordnete, die L{\"o}slichkeit von H{\"u}hnereiweis in Wasser zu steigern oder zu unterdr{\"u}cken. Die empirische Abfolge der Ionen in der Hofmeister-Serie kann jedoch bis heute nicht zweifelsfrei erkl{\"a}rt werden. Trotz weitreichender Bem{\"u}hungen, ein molekulares Verst{\"a}ndnis dieses Ph{\"a}nomens zu schaffen, konnte bisher keine Einigung {\"u}ber die zugrundeliegenden Mechanismen und die genauere Bestimmung und Lokalisierung der Wechselwirkung erzielt werden. Die resonante inelastische Weichr{\"o}ntgenstreuung (RIXS) kombiniert die beiden Methoden der R{\"o}ntgenemissions- (XES) und R{\"o}ntgenabsorptionsspektroskopie (XAS). So k{\"o}nnen mit RIXS Informationen sowohl {\"u}ber die besetzten als auch die unbesetzten elektronischen Zust{\"a}nde gesammelt und zu einem umfassenden Bild der elektronischen Struktur des Systems verkn{\"u}pft werden, was diese Methode zu einem vielversprechenden Werkzeug macht, etwas mehr Licht auf die Thematik zu werfen. Die in dieser Arbeit pr{\"a}sentierten Ergebnisse zielen deshalb darauf ab, ein verbessertes Verst{\"a}ndnis der Wechselwirkungen zwischen Salzen und Peptiden in w{\"a}ssriger L{\"o}sung zu schaffen. Hierf{\"u}r wird systematisch der Einfluss verschiedenster physikalischer Umgebungen auf die elektronische Struktur von kleinen Molek{\"u}len (Methanol und von Glycin abgeleitete Peptide) mittels Weichr{\"o}ntgenspektroskopie, unterst{\"u}tzt durch Dichtefunktionaltheorie (DFT) Rechnungen, untersucht. In einem ersten Schritt werden isolierte Molek{\"u}le ohne jeglicheWechselwirkung zu ihrer unmittelbaren Umgebung anhand von Methanol in der Gasphase als Modelsystem untersucht. Hierbei wird insbesondere der lokale und elementspezifische Charakter von RIXS demonstriert und die lokale elektronische Struktur von Methanols Hydroxyl- und Methylgruppe untersucht. Mithilfe von DFT-Rechnungen werden die beobachteten Emissionslinien in den XES-Spektren der Emission bestimmter Molek{\"u}lorbitale zugeordnet und deren relative Emissionsintensit{\"a}ten erl{\"a}utert. F{\"u}r eine resonante Anregung der ersten Resonanz an der Sauerstoff-K-Absorptionskante werden starke Isotopeneffekte beobachtet, die durch dynamische Prozesse an der Hydroxylgruppe erkl{\"a}rt werden k{\"o}nnen. Dies dient als hervorragendes Beispiel f{\"u}r m{\"o}gliche Auswirkungen, die eine lokale {\"A}nderung in der Geometrie oder Symmetrie des Molek{\"u}ls auf dessen elektronische Struktur haben kann. Im weiteren Verlauf dieser Arbeit wird das untersuchte Probensystem um die Aminos{\"a}ure Glycin und deren kleinste Peptide Diglycin und Triglycin, vorerst in ihrer kristallinen Form als Festk{\"o}rper, erweitert. Mithilfe von RIXS-Karten der Stickstoff- und Sauerstoff-K-Absorptionskanten wird erneut, unterst{\"u}tzt durch DFT-Rechnungen, ein umfassendes Bild der elektronischen Struktur der Molek{\"u}le gezeichnet. {\"A}hnlich zum Fall von Methanol werden die Emissionsspektren an der Stickstoff-K-Kante stark von dynamischen Prozessen an der protonierten Aminogruppe der Molek{\"u}le beeinflusst. Zudem wird gezeigt, dass RIXS gezielt dazu verwendet werden kann, das Stickstoffatom in der Peptidbindung anzuregen und die elektronische Struktur in dessen lokaler Umgebung zu untersuchen. Desweiteren wird ein einfaches Baukastenprinzip f{\"u}r XES-Spektren dazu genutzt, die spektralen Anteile der Emission aus {\"U}berg{\"a}ngen an den beiden Stickstoffatomen in Diglycin zu isolieren. In w{\"a}ssriger L{\"o}sung kann eine leichte Ver{\"a}nderung der elektronischen Struktur der Molek{\"u}le durch die Wechselwirkung mit benachbarten Wassermolek{\"u}len, vermutlich an den geladenen funktionellen Gruppen, beobachtet werden. Die Auswirkungen auf die XES-Spektren sind jedoch eher gering. Deutlich gr{\"o}ßere Ver{\"a}nderungen werden beobachtet, wenn man den Protonierungszustand der Molek{\"u}le {\"u}ber den pH-Wert der L{\"o}sung manipuliert. Sowohl die Protonierung der Carboxylgruppe f{\"u}r kleine pH-Werte als auch die Deprotonierung der Aminogruppe in basischer L{\"o}sung f{\"u}hren zu starken Ver{\"a}nderungen in den RIXS-Karten. In einer umfangreichen Untersuchung der XES-Spektren von Glycin als Funktion des pH-Wertes wird gezeigt, dass sich die {\"A}nderungen jedoch nicht nur {\"o}rtlich begrenzt auf die Umgebung der manipulierten funktionellen Gruppe, sondern auch auf die elektronische Struktur in weiter entfernten Bereichen des Molek{\"u}ls auswirken. Als Beispiel f{\"u}r Systeme in denen Hofmeister-Effekte beobachtet werden, werden zu guter Letzt gemischte w{\"a}ssrige L{\"o}sungen aus Diglycin und verschiedenen Salzen untersucht. Um den Einfluss verschiedener Kationen auf die elektronische Struktur der Diglycin Molek{\"u}le zu erfassen wird eine Reihe unterschiedlicher Chloride verwendet, wohingegen eine Reihe von Kaliumsalzen f{\"u}r die Untersuchung verschiedener Anionen herangezogen wird. In beiden F{\"a}llen werden ionenspezifische Auswirkungen auf die XES-Spektren von Diglycin beobachtet, die qualitativ der Sortierung innerhalb der Hofmeister-Serie folgen. Die beobachteten {\"A}nderungen deuten dabei darauf hin, dass Kationen unterschiedlich stark mit dem Sauerstoff in der Peptidbindung und dessen unmittelbarer Umgebung wechselwirken, wohingegen Anionen eine gesteigerte Affinit{\"a}t zur Aminogruppe von Diglycin aufweisen.},
  subject      = {Methanol},
  language  = {en}
}
@article{OPUS4-17335,
  title     = {Measurement of the inclusive cross-sections of single top-quark and top-antiquark \(t\)-channel production in \(pp\) collisions at \(\sqrt{s}\) = 13 TeV with the ATLAS detector},
  series = {Journal of High Energy Physics},
  volume    = {2017},
  journal   = {Journal of High Energy Physics},
  number    = {04},
  organization    = {The ATLAS Collaboration},
  doi       = {https://doi.org/10.1007/JHEP04(2017)086},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-173357},
  year      = {2017},
  abstract  = {A measurement of the \(t\)-channel single-top-quark and single-top-antiquark production cross-sections in the lepton+jets channel is presented, using 3.2 fb\(^{-1}\) of proton-proton collision data at a centre-of-mass energy of 13 TeV, recorded with the ATLAS detector at the LHC in 2015. Events are selected by requiring one charged lepton (electron or muon), missing transverse momentum, and two jets with high transverse momentum, exactly one of which is required to be \(b\)-tagged. Using a binned maximum-likelihood fit to the discriminant distribution of a neural network, the cross-sections are determined to be \({σ(tq)}\) = 156 ± 5 (stat.) ± 27 (syst.) ± 3 (lumi.) pb for single top-quark production and \(σ(\overline{t}q)\) = 91 ± 4 (stat.) ± 18 (syst.) ± 2 (lumi.) pb for single top-antiquark production, assuming a top-quark mass of 172.5 GeV. The cross-section ratio is measured to be \(R_{t}\) = \(σ(tq)/σ(\overline{t}q)\) = 1.72 ± 0.09 (stat.) ± 0.18 (syst.). All results are in agreement with Standard Model predictions.},
  language  = {en}
}
@article{OPUS4-17336,
  title     = {Measurement of charged-particle distributions sensitive to the underlying event in \(\sqrt{s}\) = 13 TeV proton-proton collisions with the ATLAS detector at the LHC},
  series = {Journal of High Energy Physics},
  volume    = {2017},
  journal   = {Journal of High Energy Physics},
  number    = {03},
  organization    = {The ATLAS Collaboration},
  doi       = {https://doi.org/10.1007/JHEP03(2017)157},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-173361},
  year      = {2017},
  abstract  = {We present charged-particle distributions sensitive to the underlying event, measured by the ATLAS detector in proton-proton collisions at a centre-of-mass energy of 13 TeV, in low-luminosity Large Hadron Collider fills corresponding to an integrated luminosity of 1.6 nb\(^{-1}\). The distributions were constructed using charged particles with absolute pseudorapidity less than 2.5 and with transverse momentum greater than 500 MeV, in events with at least one such charged particle with transverse momentum above 1 GeV. These distributions characterise the angular distribution of energy and particle flows with respect to the charged particle with highest transverse momentum, as a function of both that momentum and of charged-particle multiplicity. The results have been corrected for detector effects and are compared to the predictions of various Monte Carlo event generators, experimentally establishing the level of underlying-event activity at LHC Run 2 energies and providing inputs for the development of event generator modelling. The current models in use for UE modelling typically describe this data to 5\% accuracy, compared with data uncertainties of less than 1\%.},
  language  = {en}
}
@article{OPUS4-17278,
  title     = {Search for supersymmetry in final states with two same-sign or three leptons and jets using 36 fb\(^{-1}\) of \(\sqrt{s}=13\) TeV \(pp\) collision data with the ATLAS detector},
  series = {Journal of High Energy Physics},
  volume    = {2017},
  journal   = {Journal of High Energy Physics},
  number    = {09},
  organization    = {The ATLAS Collaboration},
  doi       = {https://doi.org/10.1007/JHEP09(2017)084},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172787},
  year      = {2017},
  abstract  = {A search for strongly produced supersymmetric particles using signatures involving multiple energetic jets and either two isolated same-sign leptons (\(e\) or \(µ\)), or at least three isolated leptons, is presented. The analysis relies on the identification of \(b\)-jets and high missing transverse momentum to achieve good sensitivity. A data sample of proton-proton collisions at \(\sqrt{s} = 13\) TeV recorded with the ATLAS detector at the Large Hadron Collider in 2015 and 2016, corresponding to a total integrated luminosity of 36.1 fb\(^{-1}\), is used for the search. No significant excess over the Standard Model prediction is observed. The results are interpreted in several simplified supersymmetric models featuring \(R\)-parity conservation or \(R\)-parity violation, extending the exclusion limits from previous searches. In models considering gluino pair production, gluino masses are excluded up to 1.87 TeV at 95\% confidence level. When bottom squarks are pair-produced and decay to a chargino and a top quark, models with bottom squark masses below 700 GeV and light neutralinos are excluded at 95\% confidence level. In addition, model-independent limits are set on a possible contribution of new phenomena to the signal region yields.},
  language  = {de}
}
@article{OPUS4-17238,
  title     = {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},
  series = {Journal of High Energy Physics},
  volume    = {2017},
  journal   = {Journal of High Energy Physics},
  number    = {191},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1007/JHEP11(2017)191},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172386},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@article{OPUS4-17239,
  title     = {Measurement of the \(t\overline{t}γ\) production cross section in proton-proton collisions at \(\sqrt{s} = 8\) TeV with the ATLAS detector},
  series = {Journal of High Energy Physics},
  volume    = {2017},
  journal   = {Journal of High Energy Physics},
  number    = {86},
  organization    = {The ATLAS Collaboration},
  doi       = {https://doi.org/10.1007/JHEP11(2017)086},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172399},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@article{OPUS4-17231,
  title     = {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},
  series = {Journal or High Energy Physics},
  volume    = {2017},
  journal   = {Journal or High Energy Physics},
  number    = {17},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1007/JHEP12(2017)017},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172310},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@article{OPUS4-17220,
  title     = {Measurement of the Drell-Yan triple-differential cross section in \(pp\) collisions at \(\sqrt{s}\) = 8 TeV},
  series = {Journal of High Energy Physics},
  volume    = {59},
  journal   = {Journal of High Energy Physics},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1007/JHEP12(2017)059},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172204},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@article{OPUS4-17350,
  title     = {Measurements of top quark spin observables in \(t\overline{t}\) events using dilepton final states in \(\sqrt{s}\) = 8 TeV \(pp\) collisions with the ATLAS detector},
  series = {Journal of High Energy Physics},
  volume    = {2017},
  journal   = {Journal of High Energy Physics},
  number    = {03},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1007/JHEP03(2017)113},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-173505},
  year      = {2017},
  abstract  = {Measurements of top quark spin observables in \(t\overline{t}\) events are presented based on 20.2 fb\(^{-1}\) of \(\sqrt{s}\) = 8 TeV proton-proton collisions recorded with the ATLAS detector at the LHC. The analysis is performed in the dilepton final state, characterised by the presence of two isolated leptons (electrons or muons). There are 15 observables, each sensitive to a different coefficient of the spin density matrix of \(t\overline{t}\) production, which are measured independently. Ten of these observables are measured for the first time. All of them are corrected for detector resolution and acceptance effects back to the parton and stable-particle levels. The measured values of the observables at parton level are compared to Standard Model predictions at next-to-leading order in QCD. The corrected distributions at stable-particle level are presented and the means of the distributions are compared to Monte Carlo predictions. No significant deviation from the Standard Model is observed for any observable.},
  language  = {en}
}
@article{OPUS4-17276,
  title     = {Top-quark mass measurement in the all-hadronic \(t\overline{t}\) decay channel at \(\sqrt{s}=8\) TeV with the ATLAS detector},
  series = {Journal of High Energy Physics},
  volume    = {2017},
  journal   = {Journal of High Energy Physics},
  number    = {09},
  organization    = {The ATLAS Collaboration},
  doi       = {https://doi.org/10.1007/JHEP09(2017)118},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172762},
  year      = {2017},
  abstract  = {The top-quark mass is measured in the all-hadronic top-antitop quark decay channel using proton-proton collisions at a centre-of-mass energy of \(\sqrt{s}=8\) TeV with the ATLAS detector at the CERN Large Hadron Collider. The data set used in the analysis corresponds to an integrated luminosity of 20.2 fb\(^{-1}\). The large multi-jet background is modelled using a data-driven method. The top-quark mass is obtained from template fits to the ratio of the three-jet to the dijet mass. The three-jet mass is obtained from the three jets assigned to the top quark decay. From these three jets the dijet mass is obtained using the two jets assigned to the W boson decay. The top-quark mass is measured to be 173.72 ± 0.55 (stat.) ± 1.01 (syst.) GeV.},
  language  = {en}
}
@article{OPUS4-17230,
  title     = {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},
  series = {Journal of High Energy Physics},
  volume    = {34},
  journal   = {Journal of High Energy Physics},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1007/JHEP12(2017)034},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172302},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@article{OPUS4-17232,
  title     = {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},
  series = {Journal of High Energy Physics},
  volume    = {2017},
  journal   = {Journal of High Energy Physics},
  number    = {195},
  organization    = {The ATLAS Collaboration},
  doi       = {10.1007/JHEP11(2017)195},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172320},
  year      = {2017},
  abstract  = {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.},
  language  = {en}
}
@article{OPUS4-17280,
  title     = {Search for new phenomena in a lepton plus high jet multiplicity final state with the ATLAS experiment using \(\sqrt{s}=13\) TeV proton-proton collision data},
  series = {Journal of High Energy Physics},
  volume    = {2017},
  journal   = {Journal of High Energy Physics},
  number    = {09},
  organization    = {The ATLAS Collaboration},
  doi       = {https://doi.org/10.1007/JHEP09(2017)088},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172802},
  year      = {2017},
  abstract  = {A search for new phenomena in final states characterized by high jet multiplicity, an isolated lepton (electron or muon) and either zero or at least three \(b\)-tagged jets is presented. The search uses 36.1 fb\(^{-1}\) of \(\sqrt{s}=13\) TeV proton-proton collision data collected by the ATLAS experiment at the Large Hadron Collider in 2015 and 2016. The dominant sources of background are estimated using parameterized extrapolations, based on observables at medium jet multiplicity, to predict the \(b\)-tagged jet multiplicity distribution at the higher jet multiplicities used in the search. No significant excess over the Standard Model expectation is observed and 95\% confidence-level limits are extracted constraining four simplified models of \(R\)-parity-violating supersymmetry that feature either gluino or top-squark pair production. The exclusion limits reach as high as 2.1 TeV in gluino mass and 1.2 TeV in top-squark mass in the models considered. In addition, an upper limit is set on the cross-section for Standard Model \(t\overline{t}t\overline{t}\) production of 60 fb (6.5 × the Standard Model prediction) at 95\% confidence level. Finally, model-independent limits are set on the contribution from new phenomena to the signal-region yields.},
  language  = {en}
}