@article{BistiRogalevKarolaketal.2017,
  author    = {Bisti, F. and Rogalev, V. A. and Karolak, M. and Paul, S. and Gupta, A. and Schmitt, T. and G{\"u}ntherodt, G. and Eyert, V. and Sangiovanni, G. and Profeta, G. and Strocov, V. N.},
  title     = {Weakly-correlated nature of ferromagnetism in nonsymmorphic CrO\(_2\) revealed by bulk-sensitive soft-X-ray ARPES},
  series = {Physical Review X},
  volume    = {7},
  journal   = {Physical Review X},
  number    = {4},
  doi       = {10.1103/PhysRevX.7.041067},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172251},
  year      = {2017},
  abstract  = {Chromium dioxide CrO\(_2\) belongs to a class of materials called ferromagnetic half-metals, whose peculiar aspect is that they act as a metal in one spin orientation and as a semiconductor or insulator in the opposite one. Despite numerous experimental and theoretical studies motivated by technologically important applications of this material in spintronics, its fundamental properties such as momentumresolved electron dispersions and the Fermi surface have so far remained experimentally inaccessible because of metastability of its surface, which instantly reduces to amorphous Cr\(_2\)O\(_3\). In this work, we demonstrate that direct access to the native electronic structure of CrO\(_2\) can be achieved with soft-x-ray angle-resolved photoemission spectroscopy whose large probing depth penetrates through the Cr\(_2\)O\(_3\) layer. For the first time, the electronic dispersions and Fermi surface of CrO\(_2\) are measured, which are fundamental prerequisites to solve the long debate on the nature of electronic correlations in this material. Since density functional theory augmented by a relatively weak local Coulomb repulsion gives an exhaustive description of our spectroscopic data, we rule out strong-coupling theories of CrO\(_2\). Crucial for the correct interpretation of our experimental data in terms of the valence-band dispersions is the understanding of a nontrivial spectral response of CrO\(_2\) caused by interference effects in the photoemission process originating from the nonsymmorphic space group of the rutile crystal structure of CrO\(_2\).},
  language  = {en}
}
@article{ErdmengerHoyosO'Bannonetal.2017,
  author    = {Erdmenger, Johanna and Hoyos, Carlos and O'Bannon, Andy and Papadimitriou, Ioannis and Probst, Jonas and Wu, Jackson M.S.},
  title     = {Two-point functions in a holographic Kondo model},
  series = {Journal of High Energy Physics},
  volume    = {3},
  journal   = {Journal of High Energy Physics},
  number    = {39},
  doi       = {10.1007/JHEP03(2017)039},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-171139},
  year      = {2017},
  abstract  = {We develop the formalism of holographic renormalization to compute two-point functions in a holographic Kondo model. The model describes a (0 + 1)-dimensional impurity spin of a gauged SU(N ) interacting with a (1 + 1)-dimensional, large-N , strongly-coupled Conformal Field Theory (CFT). We describe the impurity using Abrikosov pseudo-fermions, and define an SU(N )-invariant scalar operator O built from a pseudo-fermion and a CFT fermion. At large N the Kondo interaction is of the form O\(^{†}\)O, which is marginally relevant, and generates a Renormalization Group (RG) flow at the impurity. A second-order mean-field phase transition occurs in which O condenses below a critical temperature, leading to the Kondo effect, including screening of the impurity. Via holography, the phase transition is dual to holographic superconductivity in (1 + 1)-dimensional Anti-de Sitter space. At all temperatures, spectral functions of O exhibit a Fano resonance, characteristic of a continuum of states interacting with an isolated resonance. In contrast to Fano resonances observed for example in quantum dots, our continuum and resonance arise from a (0 + 1)-dimensional UV fixed point and RG flow, respectively. In the low-temperature phase, the resonance comes from a pole in the Green's function of the form -i〈O〉\(^{2}\), which is characteristic of a Kondo resonance.},
  language  = {en}
}
@phdthesis{Geissler2017,
  author    = {Geißler, Florian},
  title     = {Transport properties of helical Luttinger liquids},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-153450},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2017},
  abstract  = {The prediction and the experimental discovery of topological insulators has set the stage for a novel type of electronic devices. In contrast to conventional metals or semiconductors, this new class of materials exhibits peculiar transport properties at the sample surface, as conduction channels emerge at the topological boundaries of the system. In specific materials with strong spin-orbit coupling, a particular form of a two-dimensional topological insulator, the quantum spin Hall state, can be observed. Here, the respective one-dimensional edge channels are helical in nature, meaning that there is a locking of the spin orientation of an electron and its direction of motion. Due to the symmetry of time-reversal, elastic backscattering off interspersed impurities is suppressed in such a helical system, and transport is approximately ballistic. This allows in principle for the realization of novel energy-efficient devices, ``spintronic`` applications, or the formation of exotic bound states with non-Abelian statistics, which could be used for quantum computing. The present work is concerned with the general transport properties of one-dimensional helical states. Beyond the topological protection mentioned above, inelastic backscattering can arise from various microscopic sources, of which the most prominent ones will be discussed in this Thesis. As it is characteristic for one-dimensional systems, the role of electron-electron interactions can be of major importance in this context. First, we review well-established techniques of many-body physics in one dimension such as perturbative renormalization group analysis, (Abelian) bosonization, and Luttinger liquid theory. The latter allow us to treat electron interactions in an exact way. Those methods then are employed to derive the corrections to the conductance in a helical transport channel, that arise from various types of perturbations. Particularly, we focus on the interplay of Rashba spin-orbit coupling and electron interactions as a source of inelastic single-particle and two-particle backscattering. It is demonstrated, that microscopic details of the system, such as the existence of a momentum cutoff, that restricts the energy spectrum, or the presence of non-interacting leads attached to the system, can fundamentally alter the transport signature. By comparison of the predicted corrections to the conductance to a transport experiment, one can gain insight about the microscopic processes and the structure of a quantum spin Hall sample. Another important mechanism we analyze is backscattering induced by magnetic moments. Those findings provide an alternative interpretation of recent transport measurements in InAs/GaSb quantum wells.},
  subject      = {Topologischer Isolator},
  language  = {en}
}
@article{ErdmengerFernandezFloryetal.2017,
  author    = {Erdmenger, Johanna and Fern{\´a}ndez, Daniel and Flory, Mario and Meg{\´i}as, Eugenio and Straub, Ann-Kathrin and Witkowski, Piotr},
  title     = {Time evolution of entanglement for holographic steady state formation},
  series = {Journal of High Energy Physics},
  volume    = {2017},
  journal   = {Journal of High Energy Physics},
  number    = {10},
  doi       = {10.1007/JHEP10(2017)034},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-173798},
  year      = {2017},
  abstract  = {Within gauge/gravity duality, we consider the local quench-like time evolution obtained by joining two 1+1-dimensional heat baths at different temperatures at time \(t\) = 0. A steady state forms and expands in space. For the 2+1-dimensional gravity dual, we find that the "shockwaves" expanding the steady-state region are of spacelike nature in the bulk despite being null at the boundary. However, they do not transport information. Moreover, by adapting the time-dependent Hubeny-Rangamani-Takayanagi prescription, we holographically calculate the entanglement entropy and also the mutual information for different entangling regions. For general temperatures, we find that the entanglement entropy increase rate satisfies the same bound as in the 'entanglement tsunami' setups. For small temperatures of the two baths, we derive an analytical formula for the time dependence of the entanglement entropy. This replaces the entanglement tsunami-like behaviour seen for high temperatures. Finally, we check that strong subadditivity holds in this time-dependent system, as well as further more general entanglement inequalities for five or more regions recently derived for the static case.},
  language  = {en}
}
@article{AdrianMartinezAlbertAndreetal.2017,
  author    = {Adri{\´a}n-Mart{\´i}nez, S. and Albert, A. and Andr{\´e}, M. and Anghinolfi, M. and Anton, G. and Ardid, M. and Aubert, J.-J. and Baret, B. and Barrios-Marti, J. and Basa, S. and Bertin, V. and Biagi, S. and Bormuth, R. and Bouwhuis, M.C. and Bruijn, R. and Brunner, J. and Buto, J. and Capone, A. and Caramete, L. and Carr, J. and Chiarusi, T. and Circella, M. and Coniglione, R. and Costantini, H. and Coyle, P. and Creusot, A. and Dekeyser, I. and Deschamps, A. and De Bonis, G. and Distefano, C.},
  title     = {Stacked search for time shifted high energy neutrinos from gamma ray bursts with the ANTARES neutrino telescope},
  series = {European Physical Journal C},
  volume    = {77},
  journal   = {European Physical Journal C},
  number    = {1},
  doi       = {10.1140/epjc/s10052-016-4496-8},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-181251},
  pages     = {10},
  year      = {2017},
  abstract  = {A search for high-energy neutrino emission correlated with gamma-ray bursts outside the electromagnetic prompt-emission time window is presented. Using a stacking approach of the time delays between reported gamma-ray burst alerts and spatially coincident muon-neutrino signatures, data from the Antares neutrino telescope recorded between 2007 and 2012 are analysed. One year of public data from the IceCube detector between 2008 and 2009 have been also investigated. The respective timing profiles are scanned for statistically significant accumulations within 40 days of the Gamma Ray Burst, as expected from Lorentz Invariance Violation effects and some astrophysical models. No significant excess over the expected accidental coincidence rate could be found in either of the two data sets. The average strength of the neutrino signal is found to be fainter than one detectable neutrino signal per hundred gamma-ray bursts in the Antares data at 90\% confidence level.},
  language  = {en}
}
@article{TymoshenkoOnykiienkoMuelleretal.2017,
  author    = {Tymoshenko, Y. V. and Onykiienko, Y. A. and M{\"u}ller, T. and Thomale, R. and Rachel, S. and Cameron, A. S. and Portnichenko, P. Y. and Efremov, D. V. and Tsurkan, V. and Abernathy, D. L. and Ollivier, J. and Schneidewind, A. and Piovano, A. and Felea, V. and Loidl, A. and Inosov, D. S.},
  title     = {Pseudo-Goldstone magnons in the frustrated \(S=3/2\) Heisenberg helimagnet \(ZnCr_2Se_4\) with a pyrochlore magnetic sublattice},
  series = {Physical Review X},
  volume    = {7},
  journal   = {Physical Review X},
  number    = {4},
  doi       = {10.1103/PhysRevX.7.041049},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172770},
  year      = {2017},
  abstract  = {Low-energy spin excitations in any long-range ordered magnetic system in the absence of magnetocrystalline anisotropy are gapless Goldstone modes emanating from the ordering wave vectors. In helimagnets, these modes hybridize into the so-called helimagnon excitations. Here we employ neutron spectroscopy supported by theoretical calculations to investigate the magnetic excitation spectrum of the isotropic Heisenberg helimagnet \({ZnCr_2Se_4}\) with a cubic spinel structure, in which spin\(-3/2\) magnetic \({Cr^{3+}}\) ions are arranged in a geometrically frustrated pyrochlore sublattice. Apart from the conventional Goldstone mode emanating from the \((0~ 0~ {q_h})\) ordering vector, low-energy magnetic excitations in the single-domain proper-screw spiral phase show soft helimagnon modes with a small energy gap of \({∼0.17~ meV}\), emerging from two orthogonal wave vectors \(({q_h}~ 0~ 0)\) and \({(0~ {q_h}~ 0)}\) where no magnetic Bragg peaks are present. We term them pseudo-Goldstone magnons, as they appear gapless within linear spinwave theory and only acquire a finite gap due to higher-order quantum-fluctuation corrections. Our results are likely universal for a broad class of symmetric helimagnets, opening up a new way of studying weak magnon-magnon interactions with accessible spectroscopic methods.},
  language  = {en}
}
@article{LindertPozzoriniBoughezaletal.2017,
  author    = {Lindert, J. M. and Pozzorini, S. and Boughezal, R. and Campbell, J. M. and Denner, A. and Dittmaier, S. and Gehrmann-De Ridder, A. and Gehrmann, T. and Glover, N. and Huss, A. and Kallweit, S. and Maierh{\"o}fer, P. and Mangano, M. L. and Morgan, T. A. and M{\"u}ck, A. and Petriello, F. and Salam, G. P. and Sch{\"o}nherr, M. and Williams, C.},
  title     = {Precise predictions for \(V+\)jets dark matter backgrounds},
  series = {European Physical Journal C},
  volume    = {77},
  journal   = {European Physical Journal C},
  doi       = {10.1140/epjc/s10052-017-5389-1},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172555},
  year      = {2017},
  abstract  = {High-energy jets recoiling against missing transverse energy (MET) are powerful probes of dark matter at the LHC. Searches based on large MET signatures require a precise control of the \({Z(ν\overline{ν})}+\) jet background in the signal region. This can be achieved by taking accurate data in control regions dominated by \(Z(ℓ^+ℓ^-)+\) jet, \(W(ℓν)+\) jet and \(γ+\) jet production, and extrapolating to the \({Z(ν\overline{ν})}+\) jet background by means of precise theoretical predictions. In this context, recent advances in perturbative calculations open the door to significant sensitivity improvements in dark matter searches. In this spirit, we present a combination of state-of-the-art calculations for all relevant \(V+\) jets processes, including throughout NNLO QCD corrections and NLO electroweak corrections supplemented by Sudakov logarithms at two loops. Predictions at parton level are provided together with detailed recommendations for their usage in experimental analyses based on the reweighting of Monte Carlo samples. Particular attention is devoted to the estimate of theoretical uncertainties in the framework of dark matter searches, where subtle aspects such as correlations across different \(V+\) jet processes play a key role. The anticipated theoretical uncertainty in the \({Z(ν\overline{ν})}+\) jet background is at the few percent level up to the TeV range.},
  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{DennerLangUccirati2017,
  author    = {Denner, Ansgar and Lang, Jean-Nicolas and Uccirati, Sandro},
  title     = {NLO electroweak corrections in extended Higgs sectors with RECOLA2},
  series = {Journal of High Energy Physics},
  volume    = {7},
  journal   = {Journal of High Energy Physics},
  number    = {87},
  doi       = {10.1007/JHEP07(2017)087},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-170673},
  year      = {2017},
  abstract  = {We present the computer code RECOLA2 along with the first NLO electroweak corrections to Higgs production in vector-boson fusion and updated results for Higgs strahlung in the Two-Higgs-Doublet Model and Higgs-Singlet extension of the Standard Model. A fully automated procedure for the generation of tree-level and one-loop matrix elements in general models, including renormalization, is presented. We discuss the application of the Background-Field Method to the extended models. Numerical results for NLO electroweak cross sections are presented for different renormalization schemes in the Two-Higgs-Doublet Model and the Higgs-Singlet extension of the Standard Model. Finally, we present distributions for the production of a heavy Higgs boson.},
  language  = {en}
}
@article{BiedermannDennerHofer2017,
  author    = {Biedermann, Benedikt and Denner, Ansgar and Hofer, Lars},
  title     = {Next-to-leading-order electroweak corrections to the production of three charged leptons plus missing energy at the LHC},
  series = {Journal of High Energy Physics},
  volume    = {10},
  journal   = {Journal of High Energy Physics},
  number    = {43},
  doi       = {10.1007/JHEP10(2017)043},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-170219},
  year      = {2017},
  abstract  = {The production of a neutral and a charged vector boson with subsequent decays into three charged leptons and a neutrino is a very important process for precision tests of the Standard Model of elementary particles and in searches for anomalous triple-gauge-boson couplings. In this article, the first computation of next-to-leading-order electroweak corrections to the production of the four-lepton final states μ\(^{+}\)μ\(^{-}\)e\(^{+}\)ν\(_{e}\), μ\(^{+}\)μ\(^{-}\)e\(^{-}\)ν\(_{e}\), μ\(^{+}\)μ\(^{-}\)μ\(^{+}\)ν\(_{μ}\), and μ\(^{+}\)μ\(^{-}\)μ\(^{-}\)ν\(_{μ}\) at the Large Hadron Collider is presented. We use the complete matrix elements at leading and next-to-leading order, including all off-shell effects of intermediate massive vector bosons and virtual photons. The relative electroweak corrections to the fiducial cross sections from quark-induced partonic processes vary between -3\% and -6\%, depending significantly on the event selection. At the level of differential distributions, we observe large negative corrections of up to -30\% in the high-energy tails of distributions originating from electroweak Sudakov logarithms. Photon-induced contributions at next-to-leading order raise the leading-order fiducial cross section by +2\%. Interference effects in final states with equal-flavour leptons are at the permille level for the fiducial cross section, but can lead to sizeable effects in off-shell sensitive phase-space regions.},
  language  = {en}
}