@article{13515, author = {{Sanna, S. and Hölscher, R. and Schmidt, Wolf Gero}}, issn = {{0169-4332}}, journal = {{Applied Surface Science}}, pages = {{70--78}}, title = {{{Temperature dependent LiNbO3(0001): Surface reconstruction and surface charge}}}, doi = {{10.1016/j.apsusc.2014.01.104}}, year = {{2014}}, } @article{13508, author = {{Guo, Q. and Paulheim, A. and Sokolowski, M. and Aldahhak, Hazem and Rauls, E. and Schmidt, Wolf Gero}}, issn = {{1932-7447}}, journal = {{The Journal of Physical Chemistry C}}, pages = {{29911--29918}}, title = {{{Adsorption of PTCDA on Terraces and at Steps Sites of the KCl(100) Surface}}}, doi = {{10.1021/jp509663s}}, volume = {{118}}, year = {{2014}}, } @article{15864, abstract = {{Starting from the extended Su-Schrieffer-Heeger model, multiband semiconductor Bloch equations are formulated in momentum space and applied to the analysis of the linear optical response of semiconducting carbon nanotubes (SCNTs). This formalism includes the coupling of electron-hole pair excitations between different valence and conduction bands, originating from the electron-hole Coulomb attraction. The influence of these couplings, which are referred to as nondiagonal interband Coulomb interaction (NDI-CI), on the linear excitonic absorption spectra is investigated and discussed for light fields polarized parallel to the tube direction. The results show that the intervalley NDI-CI leads to a significant increase of the band gap and a decrease of the exciton binding energy that results in a blueshift of the lowest-frequency excitonic absorption peak. The strength of these effects depends on the symmetry of the SCNT. Furthermore, for zigzag SCNTs with higher symmetry other nonintervalley NDI-CI terms also affect the spectral positions of excitonic absorption peaks.}}, author = {{Liu, Hong and Schumacher, Stefan and Meier, Torsten}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, number = {{15}}, title = {{{Influence of Coulomb-induced band couplings on linear excitonic absorption spectra of semiconducting carbon nanotubes}}}, doi = {{10.1103/physrevb.89.155407}}, volume = {{89}}, year = {{2014}}, } @inproceedings{15865, author = {{Lewandowski, P. and Ardizzone, V. and Tse, Y. C. and Kwong, N. H. and Luk, M. H. and Lücke, A. and Abbarchi, M. and Bloch, J. and Baudin, E. and Galopin, E. and Lemaître, A. and Leung, P. T. and Roussignol, Ph. and Binder, R. and Tignon, J. and Schumacher, Stefan}}, booktitle = {{Ultrafast Phenomena and Nanophotonics XVIII}}, editor = {{Betz, Markus and Elezzabi, Abdulhakem Y. and Song, Jin-Joo and Tsen, Kong-Thon}}, title = {{{Formation and control of transverse patterns in a quantum fluid of microcavity polaritons}}}, doi = {{10.1117/12.2037174}}, year = {{2014}}, } @article{7485, author = {{Wiebeler, Christian and Bader, Christina A. and Meier, Cedrik and Schumacher, Stefan}}, issn = {{1463-9076}}, journal = {{Phys. Chem. Chem. Phys.}}, number = {{28}}, pages = {{14531--14538}}, publisher = {{Royal Society of Chemistry (RSC)}}, title = {{{Optical spectrum, perceived color, refractive index, and non-adiabatic dynamics of the photochromic diarylethene CMTE}}}, doi = {{10.1039/c3cp55490b}}, volume = {{16}}, year = {{2014}}, } @article{15863, author = {{Vollbrecht, Joachim and Bock, Harald and Wiebeler, Christian and Schumacher, Stefan and Kitzerow, Heinz-Siegfried}}, issn = {{0947-6539}}, journal = {{Chemistry - A European Journal}}, pages = {{12026--12031}}, title = {{{Polycyclic Aromatic Hydrocarbons Obtained by Lateral Core Extension of Mesogenic Perylenes: Absorption and Optoelectronic Properties}}}, doi = {{10.1002/chem.201403287}}, year = {{2014}}, } @article{15861, author = {{Riesen, Hans and Wiebeler, Christian and Schumacher, Stefan}}, issn = {{1089-5639}}, journal = {{The Journal of Physical Chemistry A}}, pages = {{5189--5195}}, title = {{{Optical Spectroscopy of Graphene Quantum Dots: The Case of C132}}}, doi = {{10.1021/jp502753a}}, year = {{2014}}, } @article{15862, author = {{Wiebeler, Christian and Schumacher, Stefan}}, issn = {{1089-5639}}, journal = {{The Journal of Physical Chemistry A}}, pages = {{7816--7823}}, title = {{{Quantum Yields and Reaction Times of Photochromic Diarylethenes: Nonadiabatic Ab Initio Molecular Dynamics for Normal- and Inverse-Type}}}, doi = {{10.1021/jp506316w}}, year = {{2014}}, } @inbook{18471, abstract = {{Collective spin excitations form a fundamental class of excitations in magnetic materials. As their energy reaches down to only a few meV, they are present at all temperatures and substantially influence the properties of magnetic systems. To study the spin excitations in solids from first principles, we have developed a computational scheme based on many-body perturbation theory within the full-potential linearized augmented plane-wave (FLAPW) method. The main quantity of interest is the dynamical transverse spin susceptibility or magnetic response function, from which magnetic excitations, including single-particle spin-flip Stoner excitations and collective spin-wave modes as well as their lifetimes, can be obtained. In order to describe spin waves we include appropriate vertex corrections in the form of a multiple-scattering T matrix, which describes the coupling of electrons and holes with different spins. The electron–hole interaction incorporates the screening of the many-body system within the random-phase approximation. To reduce the numerical cost in evaluating the four-point T matrix, we exploit a transformation to maximally localized Wannier functions that takes advantage of the short spatial range of electronic correlation in the partially filled d or f orbitals of magnetic materials. The theory and the implementation are discussed in detail. In particular, we show how the magnetic response function can be evaluated for arbitrary k points. This enables the calculation of smooth dispersion curves, allowing one to study fine details in the k dependence of the spin-wave spectra. We also demonstrate how spatial and time-reversal symmetry can be exploited to accelerate substantially the computation of the four-point quantities. As an illustration, we present spin-wave spectra and dispersions for the elementary ferromagnet bcc Fe, B2-type tetragonal FeCo, and CrO2 calculated with our scheme. The results are in good agreement with available experimental data.}}, author = {{Friedrich, Christoph and Şaşıoğlu, Ersoy and Müller, Mathias and Schindlmayr, Arno and Blügel, Stefan}}, booktitle = {{First Principles Approaches to Spectroscopic Properties of Complex Materials}}, editor = {{Di Valentin, Cristiana and Botti, Silvana and Cococcioni, Matteo}}, isbn = {{978-3-642-55067-6}}, issn = {{1436-5049}}, pages = {{259--301}}, publisher = {{Springer}}, title = {{{Spin excitations in solids from many-body perturbation theory}}}, doi = {{10.1007/128_2013_518}}, volume = {{347}}, year = {{2014}}, } @inbook{18472, abstract = {{Many-body perturbation theory is a well-established ab initio electronic-structure method based on Green functions. Although computationally more demanding than density functional theory, it has the distinct advantage that the exact expressions for all relevant observables, including the ground-state total energy, in terms of the Green function are known explicitly. The most important application, however, lies in the calculation of excited states, whose energies correspond directly to the poles of the Green function in the complex frequency plane. The accuracy of results obtained within this framework is only limited by the choice of the exchange-correlation self-energy, which must still be approximated in actual implementations. In this respect, the GW approximation has proved highly successful for systems governed by the Coulomb interaction. It yields band structures of solids, including the band gaps of semiconductors, as well as atomic and molecular ionization energies in very good quantitative agreement with experimental photoemission data.}}, author = {{Schindlmayr, Arno}}, booktitle = {{Many-Electron Approaches in Physics, Chemistry and Mathematics}}, editor = {{Bach, Volker and Delle Site, Luigi}}, isbn = {{978-3-319-06378-2}}, issn = {{2352-3905}}, pages = {{343--357}}, publisher = {{Springer}}, title = {{{The GW approximation for the electronic self-energy}}}, doi = {{10.1007/978-3-319-06379-9_19}}, volume = {{29}}, year = {{2014}}, } @article{18473, abstract = {{We investigate the band dispersion and related electronic properties of picene single crystals within the GW approximation for the electronic self-energy. The width of the upper highest occupied molecular orbital (HOMOu) band along the Γ–Y direction, corresponding to the b crystal axis in real space along which the molecules are stacked, is determined to be 0.60 eV and thus 0.11 eV larger than the value obtained from density-functional theory. As in our recent study of rubrene using the same methodology [S. Yanagisawa, Y. Morikawa, and A. Schindlmayr, Phys. Rev. B 88, 115438 (2013)], this increase in the bandwidth is due to the strong variation of the GW self-energy correction across the Brillouin zone, which in turn reflects the increasing hybridization of the HOMOu states of neighboring picene molecules from Γ to Y. In contrast, the width of the lower HOMO (HOMOl) band along Γ–Y remains almost unchanged, consistent with the fact that the HOMOl(Γ) and HOMOl(Y) states exhibit the same degree of hybridization, so that the nodal structure of the wave functions and the matrix elements of the self-energy correction are very similar.}}, author = {{Yanagisawa, Susumu and Morikawa, Yoshitada and Schindlmayr, Arno}}, issn = {{1347-4065}}, journal = {{Japanese Journal of Applied Physics}}, number = {{5S1}}, publisher = {{IOP Publishing and The Japan Society of Applied Physics}}, title = {{{Theoretical investigation of the band structure of picene single crystals within the GW approximation}}}, doi = {{10.7567/jjap.53.05fy02}}, volume = {{53}}, year = {{2014}}, } @inbook{18474, author = {{Friedrich, Christoph and Schindlmayr, Arno}}, booktitle = {{Computing Solids: Models, ab initio Methods and Supercomputing}}, editor = {{Blügel, Stefan and Helbig, Nicole and Meden, Volker and Wortmann, Daniel}}, isbn = {{978-3-89336-912-6}}, issn = {{1866-1807}}, location = {{Jülich}}, pages = {{A4.1--A4.21}}, publisher = {{Forschungszentrum Jülich}}, title = {{{Many-body perturbation theory: The GW approximation}}}, volume = {{74}}, year = {{2014}}, } @article{40402, author = {{Sharapova, Polina and Tikhonova, O V}}, issn = {{1742-6596}}, journal = {{Journal of Physics: Conference Series}}, keywords = {{General Physics and Astronomy}}, publisher = {{IOP Publishing}}, title = {{{Interaction of a classical laser field with a model Rydberg atom in a mixed state prepared by entanglement with few-photon quantum light}}}, doi = {{10.1088/1742-6596/497/1/012017}}, volume = {{497}}, year = {{2014}}, } @article{40400, author = {{Pérez, A. M. and Iskhakov, T. Sh. and Sharapova, Polina and Lemieux, S. and Tikhonova, O. V. and Chekhova, M. V. and Leuchs, G.}}, issn = {{0146-9592}}, journal = {{Optics Letters}}, keywords = {{Atomic and Molecular Physics, and Optics}}, number = {{8}}, publisher = {{The Optical Society}}, title = {{{Bright squeezed-vacuum source with 11 spatial mode}}}, doi = {{10.1364/ol.39.002403}}, volume = {{39}}, year = {{2014}}, } @article{43198, abstract = {{Ultrafast charge transport in strongly biased semiconductors is at the heart of high-speed electronics, electro-optics and fundamental solid-state physics1,2,3,4,5,6,7,8,9,10,11,12,13. Intense light pulses in the terahertz spectral range have opened fascinating vistas14,15,16,17,18,19,20,21. Because terahertz photon energies are far below typical electronic interband resonances, a stable electromagnetic waveform may serve as a precisely adjustable bias5,11,17,19. Novel quantum phenomena have been anticipated for terahertz amplitudes, reaching atomic field strengths8,9,10. We exploit controlled (multi-)terahertz waveforms with peak fields of 72 MV cm−1 to drive coherent interband polarization combined with dynamical Bloch oscillations in semiconducting gallium selenide. These dynamics entail the emission of phase-stable high-harmonic transients, covering the entire terahertz-to-visible spectral domain between 0.1 and 675 THz. Quantum interference of different ionization paths of accelerated charge carriers is controlled via the waveform of the driving field and explained by a quantum theory of inter- and intraband dynamics. Our results pave the way towards all-coherent terahertz-rate electronics.}}, author = {{Meier, Torsten and Schubert, O. and Hohenleutner, M. and Langer, F. and Urbanek, B. and Lange, C. and Huttner, U. and Golde, D. and Kira, M. and Koch, S. W. and Huber, R.}}, journal = {{Nature Photonics}}, number = {{2}}, publisher = {{Nature Publishing Group}}, title = {{{Sub-cycle control of terahertz high-harmonic generation by dynamical Bloch oscillations}}}, doi = {{10.1038/nphoton.2013.349}}, volume = {{8}}, year = {{2014}}, } @article{43251, abstract = {{The nonadiabatic dynamics of a many-body system driven through a quantum critical point can be controlled using counterdiabatic driving, where the formation of excitations is suppressed by assisting the dynamics with auxiliary multiple-body nonlocal interactions. We propose an alternative scheme which circumvents practical challenges to realize shortcuts to adiabaticity in mesoscopic systems by tailoring the functional form of the auxiliary counterdiabatic interactions. A driving scheme resorting in short-range few-body interactions is shown to generate an effectively adiabatic dynamics.}}, author = {{Saberi, H. and Opatrný, T. and Mølmer, K. and del Campo,, A.}}, journal = {{Physical Review A}}, number = {{6}}, title = {{{Adiabatic tracking of quantum many-body dynamics}}}, doi = {{10.1103/PhysRevA.90.060301}}, volume = {{90}}, year = {{2014}}, } @phdthesis{26522, abstract = {{In dieser Arbeit wird die Wellenausbreitung in drei verschiedenen komplexen Systemen untersucht. In den ersten beiden geht es um Wellenausbreitung in zufälligen Potentialen, einmal in einem Mikrowellenaufbau und einmal in einem akustischen Experiment. Der Fokus liegt hier auf den nicht-Gaußschen Eigenschaften der Messgrößen. Das dritte System ist ein typisches Beispiel für vollchaotische offene Systeme mit fraktalem Repeller. Damit untersuchen wir die Verbindung zwischen klassischen periodischen Bahnen und quantenmechanischen Größen. Im ersten Experiment bauen wir in die Mikrowellenkavität ein Potential ein, indem wir metallische Streukörper auf der Bodenplatte zufällig verteilen. In ortsaufgelösten Messungen können wir die gesamte Wellenfunktion untersuchen und finden starke Fluktuationen in der Intensität der Wellenfunktion. Besonders hohe Intensitäten finden sich dort, wo das analoge klassische System Kaustiken ausbildet. Außerdem wird untersucht, in welchem Abstand zur Quelle die Verästelungen starker Intensität anfangen, und ihre Skalierung bezüglich der Eigenschaften des Potentials getestet. Der vorhergesagte Exponent von $-2/3$ kann reproduziert werden. Da bei den hohen Frequenzen, bei denen gemessen wurde, mehrere Moden in der Kavität offen sind, konnten zusätzlich Effekte durch Interferenz von Moden und Koppeln zwischen Moden gefunden werden, die nicht in den theoretischen Modellen berücksichtigt sind. Erst ein störungstheoretischer Ansatz für die Helmholtz-Gleichung zeigt für nicht parallele Deckel- und Bodenplatte, dass es zusätzliche Quellterme für eine Mode durch die jeweils anderen Moden gibt. Dieser Effekt kann in dem experimentellen Daten bestätigt werden. Im zweiten Experiment mit dem akustischen Aufbau wurde der Schall, der von einer turbulenten Luftströmung verursacht wird, gemessen. Die Ergebnisse weichen stark von einer Gaußverteilung der Intensitäten ab, die der zentrale Grenzwertsatz vorhersagt. In einem zweiten Experiment in einem großen Windkanal wird zusätzlich ein Ton defnierter Frequenz durch den Luftstrom gesendet. Die Hoffnung, aus der Modulation dieses Signals Rück-schlüsse auf die Eigenschaften der Turbulenz ziehen zu können, wird nicht erfüllt. Aber wieder wird nicht-Gaußsches Verhalten gefunden. Für den dritten Teil der Arbeit kommen wieder Mikrowellenexperimente zum Einsatz, um ein weiteres komplexes System zu erforschen. Das sogenannte emph{n}-Scheiben System besteht aus emph{n} gleich-artigen Scheiben, die auf einem gleich-seitigen Polygon in einer zweidimensionalen Ebene positioniert sind. In solch offenen Systemen sind die Resonanzen nicht mehr reell, sondern komplex. Diese aus unseren Messdaten zu extrahieren, erfordert einen ausgefeilten Algorithmus, die harmonische Inversion. Die Herausforderungen der Reso-nanzextrahierung werden angesprochen und Lösungsvorschläge diskutiert. Die letztendlich erhaltenen Resonanzen werden benutzt, um die Zählfunktion der Realteile aufzustellen. Ihr Wachstum ist in führender Ordnung durch die Hausdorff-Dimension gegeben. Die Verteilung der Imaginärteile wird in Abhängigkeit der Öffnung des Systems untersucht. Der größte der aus-schließlich negativen Imaginärteile gibt die spektrale Lücke an. Diese wird mit den Vorhersagen verglichen, die auf Berechnungen über die periodischen Bahnen beruhen. Auch für die Abhängigkeit des Maximums der Verteilung von der Öffnung des Systems gibt es theoretische Annahmen, die auf ähnlichen Berechnungen beruht. Diese konnte ebenfalls unterstützt werden. Zusätzlich werden die experimentellen Resonanzen mit quantenmechanischen Berechnung verglichen.}}, author = {{Barkhofen, Sonja}}, publisher = {{Philipps-Universität Marburg}}, title = {{{Microwave Measurements on n-Disk Systems and Investigation of Branching in correlated Potentials and turbulent Flows}}}, doi = {{10.17192/Z2013.0457}}, year = {{2013}}, } @article{21041, author = {{Harder, Georg and Ansari, Vahid and Brecht, Benjamin and Dirmeier, Thomas and Marquardt, Christoph and Silberhorn, Christine}}, issn = {{1094-4087}}, journal = {{Optics Express}}, number = {{12}}, title = {{{An optimized photon pair source for quantum circuits}}}, doi = {{10.1364/oe.21.013975}}, volume = {{21}}, year = {{2013}}, } @article{21042, author = {{Christ, Andreas and Brecht, Benjamin and Mauerer, Wolfgang and Silberhorn, Christine}}, issn = {{1367-2630}}, journal = {{New Journal of Physics}}, title = {{{Theory of quantum frequency conversion and type-II parametric down-conversion in the high-gain regime}}}, doi = {{10.1088/1367-2630/15/5/053038}}, volume = {{15}}, year = {{2013}}, } @article{21043, author = {{Brecht, Benjamin and Silberhorn, Christine}}, issn = {{1050-2947}}, journal = {{Physical Review A}}, title = {{{Characterizing entanglement in pulsed parametric down-conversion using chronocyclic Wigner functions}}}, doi = {{10.1103/physreva.87.053810}}, volume = {{87}}, year = {{2013}}, }