@article{21946, abstract = {{Lithium niobate (LiNbO3), a material frequently used in optical applications, hosts different kinds of polarons that significantly affect many of its physical properties. In this study, a variety of electron polarons, namely free, bound, and bipolarons, are analyzed using first-principles calculations. We perform a full structural optimization based on density-functional theory for selected intrinsic defects with special attention to the role of symmetry-breaking distortions that lower the total energy. The cations hosting the various polarons relax to a different degree, with a larger relaxation corresponding to a larger gap between the defect level and the conduction-band edge. The projected density of states reveals that the polaron states are formerly empty Nb 4d states lowered into the band gap. Optical absorption spectra are derived within the independent-particle approximation, corrected by the GW approximation that yields a wider band gap and by including excitonic effects within the Bethe-Salpeter equation. Comparing the calculated spectra with the density of states, we find that the defect peak observed in the optical absorption stems from transitions between the defect level and a continuum of empty Nb 4d states. Signatures of polarons are further analyzed in the reflectivity and other experimentally measurable optical coefficients.}}, author = {{Schmidt, Falko and Kozub, Agnieszka L. and Gerstmann, Uwe and Schmidt, Wolf Gero and Schindlmayr, Arno}}, issn = {{2073-4352}}, journal = {{Crystals}}, pages = {{542}}, publisher = {{MDPI}}, title = {{{Electron polarons in lithium niobate: Charge localization, lattice deformation, and optical response}}}, doi = {{10.3390/cryst11050542}}, volume = {{11}}, year = {{2021}}, } @inproceedings{43746, abstract = {{Population/mixing-time-dependent two-dimensional coherent spectra are presented for exciton-polaritons in a microcavity. Theory based on dynamically-controlled truncation reveals coherent and incoherent contributions to the decay dynamics.}}, author = {{Meier, Torsten and Paul, Jagannath and Rose, Hendrik and Wahlstrand, Jared K and Bristow, Alan D}}, booktitle = {{Frontiers in Optics}}, isbn = {{978-1-55752-308-2}}, location = {{Washington, DC United States}}, publisher = {{Frontiers in Optics}}, title = {{{Coherent and incoherent contribution of population dynamics of semiconductor exciton-polaritons}}}, doi = {{10.1364/FIO.2021.FW5C.6}}, year = {{2021}}, } @inproceedings{23474, author = {{Reichelt, Matthias and Rose, Hendrik and Kosarev, Alexander N. and Poltavtsev, Sergey V. and Bayer, Manfred and Akimov, Ilya A. and Schneider, Christian and Kamp, Martin and Höfling, Sven and Meier, Torsten}}, booktitle = {{Ultrafast Phenomena and Nanophotonics XXV}}, editor = {{Betz, Markus and Elezzabi, Abdulhakem Y.}}, title = {{{Controlling the emission time of photon echoes by optical freezing of exciton dephasing and rephasing in quantum-dot ensembles}}}, doi = {{10.1117/12.2576887}}, volume = {{11684}}, year = {{2021}}, } @article{29749, author = {{Murzakhanov, F. F. and Yavkin, B. V. and Mamin, G. V. and Orlinskii, S. B. and von Bardeleben, H. J. and Biktagirov, Timur and Gerstmann, Uwe and Soltamov, V. A.}}, issn = {{2469-9950}}, journal = {{Physical Review B}}, pages = {{245203}}, publisher = {{American Physical Society (APS)}}, title = {{{Hyperfine and nuclear quadrupole splitting of the NV− ground state in 4H-SiC}}}, doi = {{10.1103/physrevb.103.245203}}, volume = {{103}}, year = {{2021}}, } @article{22010, author = {{Aldahhak, Hazem and Hogan, Conor and Lindner, Susi and Appelfeller, Stephan and Eisele, Holger and Schmidt, Wolf Gero and Dähne, Mario and Gerstmann, Uwe and Franz, Martin}}, issn = {{2469-9950}}, journal = {{Physical Review B}}, pages = {{035303}}, title = {{{Electronic structure of the Si(111)3×3R30∘−B surface from theory and photoemission spectroscopy}}}, doi = {{10.1103/physrevb.103.035303}}, volume = {{103}}, year = {{2021}}, } @article{23478, author = {{Rose, Hendrik and Popolitova, D. V. and Tikhonova, O. V. and Meier, Torsten and Sharapova, Polina}}, issn = {{2469-9926}}, journal = {{Physical Review A}}, title = {{{Dark-state and loss-induced phenomena in the quantum-optical regime of Λ-type three-level systems}}}, doi = {{10.1103/physreva.103.013702}}, volume = {{103}}, year = {{2021}}, } @article{23473, author = {{Belobo, Didier Belobo and Meier, Torsten}}, issn = {{1367-2630}}, journal = {{New Journal of Physics}}, title = {{{Approximate nonlinear wave solutions of the coupled two-component Gross–Pitaevskii equations with spin–orbit interaction}}}, doi = {{10.1088/1367-2630/abf3ed}}, volume = {{23}}, year = {{2021}}, } @article{22881, author = {{Nguyen, T. T. Nhung and Sollfrank, T. and Tegenkamp, C. and Rauls, E. and Gerstmann, Uwe}}, issn = {{2469-9950}}, journal = {{Physical Review B}}, pages = {{L201408}}, title = {{{Impact of screening and relaxation on weakly coupled two-dimensional heterostructures}}}, doi = {{10.1103/physrevb.103.l201408}}, volume = {{103}}, year = {{2021}}, } @article{21635, abstract = {{Modern forming processes often allow today the efficient production of complex parts. In order to increase the sustainability of forming processes it would be favorable if the forming of workpieces becomes possible using production waste. At the Chair of Forming and Machining Technology of the Paderborn University (LUF) research is presently conducted with the overall goal to produce workpieces directly from secondary aluminum (e.g., powder and chips). Therefore, friction-based forming processes like friction spinning (or cognate processes) are used due to their high efficiency. As a pre-step, the production of semi-finished parts was the subject of accorded research work at the LUF. Therefore, a friction-based hot extrusion process was used for the full recycling or rework of aluminum chips into profiles. Investigations of the recycled semi-finished products show that they are comparable to conventionally produced semi-finished products in terms of dimensional stability and shape accuracy. An analysis of the mechanical properties of hardness and tensile strength shows that a final product with good and homogeneously distributed properties can be produced. Furthermore, significant correlations to the friction spinning process could be found that are useful for the above-mentioned direct part production from secondary aluminum.}}, author = {{Borgert, Thomas and Homberg, Werner}}, issn = {{2075-4701}}, journal = {{Metals}}, title = {{{Friction-Induced Recycling Process for User-Specific Semi-Finished Product Production}}}, doi = {{10.3390/met11040663}}, year = {{2021}}, } @inproceedings{23746, author = {{Moritzer, Elmar and Flachmann, Felix}}, booktitle = {{SPE ANTEC 2021: The Annual Technical Conference for Plastic Professionals}}, isbn = {{978-1-7138-3075-7}}, location = {{Online}}, pages = {{536--540}}, title = {{{Influence of Chemical Blowing Agents on the Filling Behavior of Wood-Plastic-Composite Melts}}}, year = {{2021}}, }