@inproceedings{16959, author = {{Ferreri, A. and Sharapova, P. and Luo, Kai Hong and Herrmann, H. and Silberhorn, C.}}, booktitle = {{Quantum Information and Measurement (QIM) V: Quantum Technologies}}, isbn = {{9781943580569}}, keywords = {{pc2-ressources}}, title = {{{Theoretical description of a multimode SU(1,1) interferometer}}}, doi = {{10.1364/qim.2019.t5a.35}}, year = {{2019}}, } @unpublished{16945, author = {{Riabinin, Matvei and Sharapova, Polina and Bartley, Tim and Meier, Torsten}}, keywords = {{pc2-ressources}}, title = {{{Generating two-mode squeezing and Schrödinger cat states with multimode measurement-induced nonlinearity}}}, year = {{2019}}, } @article{10014, abstract = {{The cubic, tetragonal, and orthorhombic phase of potassium niobate (KNbO3) are studied based on density-functional theory. Starting from the relaxed atomic geometries, we analyze the influence of self-energy corrections on the electronic band structure within the GW approximation. We find that quasiparticle shifts widen the direct (indirect) band gap by 1.21 (1.44), 1.58 (1.55), and 1.67 (1.64) eV for the cubic, tetragonal, and orthorhombic phase, respectively. By solving the Bethe-Salpeter equation, we obtain the linear dielectric function with excitonic and local-field effects, which turn out to be essential for good agreement with experimental data. From our results, we extract an exciton binding energy of 0.6, 0.5, and 0.5 eV for the cubic, tetragonal, and orthorhombic phase, respectively. Furthermore, we investigate the nonlinear second-harmonic generation (SHG) both theoretically and experimentally. The frequency-dependent second-order polarization tensor of orthorhombic KNbO3 is measured for incoming photon energies between 1.2 and 1.6 eV. In addition, calculations within the independent-(quasi)particle approximation are performed for the tetragonal and orthorhombic phase. The novel experimental data are in excellent agreement with the quasiparticle calculations and resolve persistent discrepancies between earlier experimental measurements and ab initio results reported in the literature.}}, author = {{Schmidt, Falko and Riefer, Arthur and Schmidt, Wolf Gero and Schindlmayr, Arno and Imlau, Mirco and Dobener, Florian and Mengel, Nils and Chatterjee, Sangam and Sanna, Simone}}, issn = {{2475-9953}}, journal = {{Physical Review Materials}}, number = {{5}}, publisher = {{American Physical Society}}, title = {{{Quasiparticle and excitonic effects in the optical response of KNbO3}}}, doi = {{10.1103/PhysRevMaterials.3.054401}}, volume = {{3}}, year = {{2019}}, } @article{29746, author = {{Nicholson, C. W. and Puppin, M. and Lücke, A. and Gerstmann, Uwe and Krenz, Marvin and Schmidt, Wolf Gero and Rettig, L. and Ernstorfer, R. and Wolf, M.}}, issn = {{2469-9950}}, journal = {{Physical Review B}}, number = {{15}}, publisher = {{American Physical Society (APS)}}, title = {{{Excited-state band mapping and momentum-resolved ultrafast population dynamics in In/Si(111) nanowires investigated with XUV-based time- and angle-resolved photoemission spectroscopy}}}, doi = {{10.1103/physrevb.99.155107}}, volume = {{99}}, year = {{2019}}, } @article{10015, author = {{Dues, Christof and Schmidt, Wolf Gero and Sanna, Simone}}, issn = {{2470-1343}}, journal = {{ACS Omega}}, pages = {{3850--3859}}, title = {{{Water Splitting Reaction at Polar Lithium Niobate Surfaces}}}, doi = {{10.1021/acsomega.8b03271}}, year = {{2019}}, } @article{37288, abstract = {{An integrated chip with quantum state generation, active polarization manipulation, and precise time control is demonstrated.}}, author = {{Luo, Kai-Hong and Brauner, Sebastian and Eigner, Christof and Sharapova, Polina and Ricken, Raimund and Meier, Torsten and Herrmann, Harald and Silberhorn, Christine}}, issn = {{2375-2548}}, journal = {{Science Advances}}, keywords = {{Multidisciplinary}}, number = {{1}}, publisher = {{American Association for the Advancement of Science (AAAS)}}, title = {{{Nonlinear integrated quantum electro-optic circuits}}}, doi = {{10.1126/sciadv.aat1451}}, volume = {{5}}, year = {{2019}}, } @inproceedings{13285, author = {{Hannes, Wolf-Rüdiger and Krauß-Kodytek, Laura and Ruppert, Claudia and Betz, Markus and Meier, Torsten}}, booktitle = {{Ultrafast Phenomena and Nanophotonics XXIII}}, editor = {{Betz, Markus and Elezzabi, Abdulhakem Y.}}, isbn = {{9781510624740}}, title = {{{Intensity-dependent degenerate and non-degenerate nonlinear optical absorption of direct-gap semiconductors}}}, doi = {{10.1117/12.2503539}}, volume = {{10916}}, year = {{2019}}, } @article{13284, author = {{Hannes, Wolf-Rüdiger and Meier, Torsten}}, issn = {{2469-9950}}, journal = {{Physical Review B}}, number = {{12}}, title = {{{Higher-order contributions and nonperturbative effects in the nondegenerate nonlinear optical absorption of semiconductors using a two-band model}}}, doi = {{10.1103/physrevb.99.125301}}, volume = {{99}}, year = {{2019}}, } @article{13365, abstract = {{The KTiOPO4 (KTP) band structure and dielectric function are calculated on various levels of theory starting from density-functional calculations. Within the independent-particle approximation an electronic transport gap of 2.97 eV is obtained that widens to about 5.23 eV when quasiparticle effects are included using the GW approximation. The optical response is shown to be strongly anisotropic due to (i) the slight asymmetry of the TiO6 octahedra in the (001) plane and (ii) their anisotropic distribution along the [001] and [100] directions. In addition, excitonic effects are very important: The solution of the Bethe–Salpeter equation indicates exciton binding energies of the order of 1.5 eV. Calculations that include both quasiparticle and excitonic effects are in good agreement with the measured reflectivity.}}, author = {{Neufeld, Sergej and Bocchini, Adriana and Gerstmann, Uwe and Schindlmayr, Arno and Schmidt, Wolf Gero}}, issn = {{2515-7639}}, journal = {{Journal of Physics: Materials}}, pages = {{045003}}, publisher = {{IOP Publishing}}, title = {{{Potassium titanyl phosphate (KTP) quasiparticle energies and optical response}}}, doi = {{10.1088/2515-7639/ab29ba}}, volume = {{2}}, year = {{2019}}, } @article{13900, author = {{Song, Xiaohong and Zuo, Ruixin and Yang, Shidong and Li, Pengcheng and Meier, Torsten and Yang, Weifeng}}, issn = {{1094-4087}}, journal = {{Optics Express}}, number = {{3}}, pages = {{2225--2234}}, title = {{{Attosecond temporal confinement of interband excitation by intraband motion}}}, doi = {{10.1364/oe.27.002225}}, volume = {{27}}, year = {{2019}}, } @article{13283, author = {{Duc, Huynh Thanh and Ngo, Cong and Meier, Torsten}}, issn = {{2469-9950}}, journal = {{Physical Review B}}, number = {{4}}, title = {{{Ballistic photocurrents in semiconductor quantum wells caused by the excitation of asymmetric excitons}}}, doi = {{10.1103/physrevb.100.045308}}, volume = {{100}}, year = {{2019}}, } @article{13429, author = {{Bocchini, Adriana and Neufeld, Sergej and Gerstmann, Uwe and Schmidt, Wolf Gero}}, issn = {{0953-8984}}, journal = {{Journal of Physics: Condensed Matter}}, pages = {{385401}}, title = {{{Oxygen and potassium vacancies in KTP calculated from first principles}}}, doi = {{10.1088/1361-648x/ab295c}}, volume = {{31}}, year = {{2019}}, } @article{21, abstract = {{We address the general mathematical problem of computing the inverse p-th root of a given matrix in an efficient way. A new method to construct iteration functions that allow calculating arbitrary p-th roots and their inverses of symmetric positive definite matrices is presented. We show that the order of convergence is at least quadratic and that adaptively adjusting a parameter q always leads to an even faster convergence. In this way, a better performance than with previously known iteration schemes is achieved. The efficiency of the iterative functions is demonstrated for various matrices with different densities, condition numbers and spectral radii.}}, author = {{Richters, Dorothee and Lass, Michael and Walther, Andrea and Plessl, Christian and Kühne, Thomas}}, journal = {{Communications in Computational Physics}}, number = {{2}}, pages = {{564--585}}, publisher = {{Global Science Press}}, title = {{{A General Algorithm to Calculate the Inverse Principal p-th Root of Symmetric Positive Definite Matrices}}}, doi = {{10.4208/cicp.OA-2018-0053}}, volume = {{25}}, year = {{2019}}, } @inbook{13436, author = {{Camberg, Alan Adam and Stratmann, Ina and Tröster, Thomas}}, booktitle = {{Technologies for economical and functional lightweight design}}, isbn = {{9783662582053}}, issn = {{2524-4787}}, title = {{{TAILORED STACKED HYBRIDS – AN OPTIMIZATION-BASED APPROACH IN MATERIAL DESIGN FOR FURTHER IMPROVEMENT IN LIGHTWEIGHT CAR BODY STRUCTURES}}}, doi = {{10.1007/978-3-662-58206-0_12}}, year = {{2019}}, } @article{15739, author = {{Azadi, Sam and Kühne, Thomas D.}}, issn = {{2469-9950}}, journal = {{Physical Review B}}, number = {{15}}, pages = {{155103--155109}}, title = {{{Unconventional phase III of high-pressure solid hydrogen}}}, doi = {{10.1103/physrevb.100.155103}}, volume = {{100}}, year = {{2019}}, } @article{15851, author = {{Ma, Xuekai and Kartashov, Yaroslav Y and Gao, Tingge and Schumacher, Stefan}}, issn = {{1367-2630}}, journal = {{New Journal of Physics}}, title = {{{Controllable high-speed polariton waves in a PT-symmetric lattice}}}, doi = {{10.1088/1367-2630/ab5a9b}}, volume = {{21}}, year = {{2019}}, } @unpublished{13340, abstract = {{Spontaneous formation of transverse patterns is ubiquitous in nonlinear dynamical systems of all kinds. An aspect of particular interest is the active control of such patterns. In nonlinear optical systems this can be used for all-optical switching with transistor-like performance, for example realized with polaritons in a planar quantum-well semiconductor microcavity. Here we focus on a specific configuration which takes advantage of the intricate polarization dependencies in the interacting optically driven polariton system. Besides detailed numerical simulations of the coupled light-field exciton dynamics, in the present paper we focus on the derivation of a simplified population competition model giving detailed insight into the underlying mechanisms from a nonlinear dynamical systems perspective. We show that such a model takes the form of a generalized Lotka-Volterra system for two competing populations explicitly including a source term that enables external control. We present a comprehensive analysis both of the existence and stability of stationary states in the parameter space spanned by spatial anisotropy and external control strength. We also construct phase boundaries in non-trivial regions and characterize emerging bifurcations. The population competition model reproduces all key features of the switching observed in full numerical simulations of the rather complex semiconductor system and at the same time is simple enough for a fully analytical understanding of the system dynamics.}}, author = {{Pukrop, Matthias and Schumacher, Stefan}}, booktitle = {{arXiv:1903.12534}}, title = {{{Externally Controlled Lotka-Volterra Dynamics in a Linearly Polarized Polariton Fluid}}}, year = {{2019}}, } @unpublished{13347, abstract = {{<div> <div> <div> <p>Molecular doping in conjugated polymers is a crucial process for their application in organic photovoltaics and optoelectronics. In the present work we theoretically investigate p-type molecu- lar doping in a series of (poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b”]dithiophene)-alt- 4,7-(2,1,3-benzothiadiazole)] (PCPDT-BT) conjugated oligomers with different lengths and three widely-used dopants with different electron affinities, namely F4TCNQ, F6TCNNQ, and CN6-CP. We study in detail the molecular geometry of possible oligomer-dopant complexes and its influence on the doping mechanisms and electronic system properties. We find that the mechanisms of dop- ing and charge transfer observed sensitively depend on the specific geometry of the oligomer-dopant complexes. For a given complex different geometries may exist, some of which show transfer of an entire electron from the oligomer chain onto the dopant molecule resulting in an integer-charge transfer complex, leaving the system in a ground state with broken spin symmetry. In other ge- ometries merely hybridization of oligomer and dopant frontier orbitals occurs with partial charge transfer but spin-symmetric ground state. Considering the resulting electronic density of states both cases may well contribute to an increased electrical conductivity of corresponding film samples while the underlying physical mechanisms are entirely different. </p> </div> </div> </div>}}, author = {{Dong, Chuan-Ding and Schumacher, Stefan}}, title = {{{Molecular Doping of PCPDT-BT Copolymers: Comparison of Molecular Complexes with and Without Integer Charge Transfer}}}, year = {{2019}}, } @article{13343, author = {{Vollbrecht, Joachim and Wiebeler, Christian and Bock, Harald and Schumacher, Stefan and Kitzerow, Heinz-Siegfried}}, issn = {{1932-7447}}, journal = {{The Journal of Physical Chemistry C}}, number = {{7}}, pages = {{4483--4492}}, title = {{{Curved Polar Dibenzocoronene Esters and Imides versus Their Planar Centrosymmetric Homologs: Photophysical and Optoelectronic Analysis}}}, doi = {{10.1021/acs.jpcc.8b10730}}, volume = {{123}}, year = {{2019}}, } @inproceedings{58921, author = {{De Matteis, Tiziano and de Fine Licht, Johannes and Beránek, Jakub and Hoefler, Torsten}}, booktitle = {{Proceedings of the International Conference for High Performance Computing, Networking, Storage and Analysis}}, publisher = {{ACM}}, title = {{{Streaming message interface}}}, doi = {{10.1145/3295500.3356201}}, year = {{2019}}, }