@article{13830, author = {{Rauls, E. and Wiebe, J. and Schmidt, Wolf Gero}}, issn = {{0022-0248}}, journal = {{Journal of Crystal Growth}}, pages = {{2892--2895}}, title = {{{Understanding the cubic AlN growth plane from first principles}}}, doi = {{10.1016/j.jcrysgro.2010.07.027}}, volume = {{312}}, year = {{2010}}, } @article{13834, author = {{Sanna, Simone and Schmidt, Wolf Gero}}, issn = {{0169-4332}}, journal = {{Applied Surface Science}}, pages = {{5740--5743}}, title = {{{GaN/LiNbO3 (0001) interface formation calculated from first-principles}}}, doi = {{10.1016/j.apsusc.2010.03.098}}, volume = {{256}}, year = {{2010}}, } @article{13826, author = {{Blankenburg, S. and Rauls, E. and Schmidt, Wolf Gero}}, issn = {{1948-7185}}, journal = {{The Journal of Physical Chemistry Letters}}, pages = {{3266--3270}}, title = {{{Catalytic Action of a Cu(111) Surface on Tetraazaperopyrene Polymerization}}}, doi = {{10.1021/jz101389u}}, volume = {{1}}, year = {{2010}}, } @article{15846, author = {{Schumacher, Stefan and Galbraith, Ian and Ruseckas, Arvydas and Turnbull, Graham A. and Samuel, Ifor D. W.}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, title = {{{Dynamics of photoexcitation and stimulated optical emission in conjugated polymers: A multiscale quantum-chemistry and Maxwell-Bloch-equations approach}}}, doi = {{10.1103/physrevb.81.245407}}, year = {{2010}}, } @article{18562, abstract = {{The structural and electronic properties of strained silicon are investigated quantitatively with ab initio computational methods. For this purpose we combine densityfunctional theory within the local‐density approximation and the GW approximation for the electronic self‐energy. From the variation of the total energy as a function of applied strain we obtain the elastic constants, Poisson ratios and related structural parameters, taking a possible internal relaxation fully into account. For biaxial tensile strain in the (001) and (111) planes we then investigate the effects on the electronic band structure. These strain configurations occur in epitaxial silicon films grown on SiGe templates along different crystallographic directions. The tetragonal deformation resulting from (001) strain induces a valley splitting that removes the sixfold degeneracy of the conduction‐band minimum. Furthermore, strain in any direction causes the band structure to warp. We present quantitative results for the electron effective mass, derived from the curvature of the conduction band, as a function of strain and discuss the implications for the mobility of the charge carriers. The inclusion of proper self‐energy corrections within the GW approximation in our work not only yields band gaps in much better agreement with experimental measurements than the localdensity approximation, but also predicts slightly larger electron effective masses.}}, author = {{Bouhassoune, Mohammed and Schindlmayr, Arno}}, issn = {{1610-1642}}, journal = {{Physica Status Solidi C}}, location = {{Weimar}}, number = {{2}}, pages = {{460--463}}, publisher = {{Wiley-VCH}}, title = {{{Electronic structure and effective masses in strained silicon}}}, doi = {{10.1002/pssc.200982470}}, volume = {{7}}, year = {{2010}}, } @inbook{18549, abstract = {{We describe the software package SPEX, which allows first-principles calculations of quasiparticle and collective electronic excitations in solids using techniques from many-body perturbation theory. The implementation is based on the full-potential linearized augmented-plane-wave (FLAPW) method, which treats core and valence electrons on an equal footing and can be applied to a wide range of materials, including transition metals and rare earths. After a discussion of essential features that contribute to the high numerical efficiency of the code, we present illustrative results for quasiparticle band structures calculated within the GW approximation for the electronic self-energy, electron-energy-loss spectra with inter- and intraband transitions as well as local-field effects, and spin-wave spectra of itinerant ferromagnets. In all cases the inclusion of many-body correlation terms leads to very good quantitative agreement with experimental spectroscopies.}}, author = {{Schindlmayr, Arno and Friedrich, Christoph and Şaşıoğlu, Ersoy and Blügel, Stefan}}, booktitle = {{Modern and Universal First-Principles Methods for Many-Electron Systems in Chemistry and Physics}}, editor = {{Dolg, Franz Michael}}, isbn = {{978-3-486-59827-8}}, pages = {{67--78}}, publisher = {{Oldenbourg}}, title = {{{First-principles calculation of electronic excitations in solids with SPEX}}}, doi = {{10.1524/9783486711639.67}}, volume = {{3}}, year = {{2010}}, } @article{18560, abstract = {{We present a computational scheme to study spin excitations in magnetic materials from first principles. The central quantity is the transverse spin susceptibility, from which the complete excitation spectrum, including single-particle spin-flip Stoner excitations and collective spin-wave modes, can be obtained. The susceptibility is derived from many-body perturbation theory and includes dynamic correlation through a summation over ladder diagrams that describe the coupling of electrons and holes with opposite spins. In contrast to earlier studies, we do not use a model potential with adjustable parameters for the electron-hole interaction but employ the random-phase approximation. To reduce the numerical cost for the calculation of the four-point scattering matrix we perform a projection onto maximally localized Wannier functions, which allows us to truncate the matrix efficiently by exploiting the short spatial range of electronic correlation in the partially filled d or f orbitals. Our implementation is based on the full-potential linearized augmented-plane-wave method. Starting from a ground-state calculation within the local-spin-density approximation (LSDA), we first analyze the matrix elements of the screened Coulomb potential in the Wannier basis for the 3d transition-metal series. In particular, we discuss the differences between a constrained nonmagnetic and a proper spin-polarized treatment for the ferromagnets Fe, Co, and Ni. The spectrum of single-particle and collective spin excitations in fcc Ni is then studied in detail. The calculated spin-wave dispersion is in good overall agreement with experimental data and contains both an acoustic and an optical branch for intermediate wave vectors along the [100] direction. In addition, we find evidence for a similar double-peak structure in the spectral function along the [111] direction. To investigate the influence of static correlation we finally consider LSDA+U as an alternative starting point and show that, together with an improved description of the Fermi surface, it yields a more accurate quantitative value for the spin-wave stiffness constant, which is overestimated in the LSDA.}}, author = {{Şaşıoğlu, Ersoy and Schindlmayr, Arno and Friedrich, Christoph and Freimuth, Frank and Blügel, Stefan}}, issn = {{1550-235X}}, journal = {{Physical Review B}}, number = {{5}}, publisher = {{American Physical Society}}, title = {{{Wannier-function approach to spin excitations in solids}}}, doi = {{10.1103/PhysRevB.81.054434}}, volume = {{81}}, year = {{2010}}, } @article{18557, abstract = {{We describe the software package SPEX, which allows first-principles calculations of quasiparticle and collective electronic excitations in solids using techniques from many-body perturbation theory. The implementation is based on the full-potential linearized augmented-plane-wave (FLAPW) method, which treats core and valence electrons on an equal footing and can be applied to a wide range of materials, including transition metals and rare earths. After a discussion of essential features that contribute to the high numerical efficiency of the code, we present illustrative results for quasiparticle band structures calculated within the GW approximation for the electronic self-energy, electron-energy-loss spectra with inter- and intraband transitions as well as local-field effects, and spin-wave spectra of itinerant ferromagnets. In all cases the inclusion of many-body correlation terms leads to very good quantitative agreement with experimental spectroscopies.}}, author = {{Schindlmayr, Arno and Friedrich, Christoph and Şaşıoğlu, Ersoy and Blügel, Stefan}}, issn = {{2196-7156}}, journal = {{Zeitschrift für Physikalische Chemie}}, number = {{3-4}}, pages = {{357--368}}, publisher = {{Oldenbourg}}, title = {{{First-principles calculation of electronic excitations in solids with SPEX}}}, doi = {{10.1524/zpch.2010.6110}}, volume = {{224}}, year = {{2010}}, } @article{4177, abstract = {{Excitonic spectra of weakly disordered semiconductor heterostructures are simulated on the basis of a one-dimensional tight-binding model. The influence of the length scale of weak disorder in quantum wells on the redshift of the excitonic peak and its linewidth is studied. By calculating two-dimensional Fouriertransform spectra we are able to determine the contribution of disorder to inhomogeneous and also to homogeneous broadenings separately. This disorder-induced dephasing is related to a Fano-type coupling and leads to contributions to the homogeneous linewidth that depends on energy within the inhomogeneously broadened line. The model includes heavy- and light-hole excitons and yields smaller inhomogeneous broadening for the light-hole exciton if compared to the heavy-hole exciton, which agrees qualitatively with the experiment.}}, author = {{Kuznetsova, I. and Gőgh, N. and Förstner, Jens and Meier, Torsten and Cundiff, S. T. and Varga, I. and Thomas, P.}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, keywords = {{tet_topic_qw}}, number = {{7}}, publisher = {{American Physical Society (APS)}}, title = {{{Modeling excitonic line shapes in weakly disordered semiconductor nanostructures}}}, doi = {{10.1103/physrevb.81.075307}}, volume = {{81}}, year = {{2010}}, } @article{4125, abstract = {{We numerically investigate the behavior of Whispering Gallery Modes (WGMs) in circularly shaped resonators like microdisks, with diameters in the range of optical vacuum wavelengths. The microdisk is embedded in an uniaxial anisotropic dielectric environment. By changing the optical anisotropy, one obtains spectral tunability of the optical modes. The degree of tunability strongly depends on the radial (azimuthal) mode order M (N). As the modes approach each other spectrally, anticrossing is observed, leading to a rearrangement of the optical states.}}, author = {{Declair, S. and Meier, Cedrik and Meier, Torsten and Förstner, Jens}}, issn = {{1569-4410}}, journal = {{Photonics and Nanostructures - Fundamentals and Applications}}, keywords = {{tet_topic_microdisk}}, number = {{4}}, pages = {{273--277}}, publisher = {{Elsevier BV}}, title = {{{Anticrossing of Whispering Gallery Modes in microdisk resonators embedded in an anisotropic environment}}}, doi = {{10.1016/j.photonics.2010.03.002}}, volume = {{8}}, year = {{2010}}, } @article{4547, abstract = {{The coherent state manipulation of single quantum systems is a fundamental requirement for the implementation of quantum information processors. Exciton qubits are of particular interest for coherent optoelectronic applications, in particular due to their excellent coupling to photons. Until now, coherent manipulations of exciton qubits in semiconductor quantum dots have been performed predominantly by pulsed laser fields. Coherent control of the population of excitonic states with a single laser pulse, observed by Rabi oscillations, has been demonstrated by several groups using different techniques1,2,3. By using two laser pulses, more general state control can be achieved4, and coupling of two excitons has been reported5,6. Here, we present a conceptually new approach for implementing the coherent control of an exciton two-level system (qubit) by means of a time-dependent electric interaction. The new scheme makes use of an optical clock signal and a synchronous electric gate signal, which controls the coherent manipulation.}}, author = {{Michaelis de Vasconcellos, S. and Gordon, S. and Bichler, M. and Meier, Torsten and Zrenner, Artur}}, issn = {{1749-4885}}, journal = {{Nature Photonics}}, number = {{8}}, pages = {{545--548}}, publisher = {{Springer Nature}}, title = {{{Coherent control of a single exciton qubit by optoelectronic manipulation}}}, doi = {{10.1038/nphoton.2010.124}}, volume = {{4}}, year = {{2010}}, } @article{4123, abstract = {{GaAs-based semiconductor microdisks with high quality whispering gallery modes (Q44000) have been fabricated.A layer of self-organized InAs quantumdots (QDs) served as a light source to feed the optical modes at room temperature. In order to achieve frequency tuning of the optical modes, the microdisk devices have been immersed in 4 – cyano – 4´-pentylbiphenyl (5CB), a liquid crystal(LC) with a nematic phase below the clearing temperature of TC≈34°C .We have studied the device performance in the temperature rangeof T=20-50°C, in order to investigate the influence of the nematic–isotropic phase transition on the optical modes. Moreover,we havea pplied an AC electric field to the device,which leads in the nematic phase to a reorientation of the anisotropic dielectric tensor of the liquid crystal.This electrical anisotropy can be used to achieve electrical tunability of the optical modes.Using the finite-difference time domain (FDTD) technique with an anisotropic material model, we are able to describe the influence of the liquid crystal qualitatively.}}, author = {{Piegdon, Karoline A. and Offer, Matthias and Lorke, Axel and Urbanski, Martin and Hoischen, Andreas and Kitzerow, Heinz-Siegfried and Declair, Stefan and Förstner, Jens and Meier, Torsten and Reuter, Dirk and Wieck, Andreas D. and Meier, Cedrik}}, issn = {{1386-9477}}, journal = {{Physica E: Low-dimensional Systems and Nanostructures}}, keywords = {{tet_topic_qd, tet_topic_microdisk}}, number = {{10}}, pages = {{2552--2555}}, publisher = {{Elsevier BV}}, title = {{{Self-assembled quantum dots in a liquid-crystal-tunable microdisk resonator}}}, doi = {{10.1016/j.physe.2009.12.051}}, volume = {{42}}, year = {{2010}}, } @article{4169, abstract = {{It is demonstrated that valence-band mixing in GaAs quantum wells tremendously modifies electronic transport. A coherent control scheme in which ultrafast currents are optically injected into undoped GaAs quantum wells upon excitation with femtosecond laser pulses is employed. An oscillatory dependence of the injection current amplitude and direction on the excitation photon energy is observed. A microscopic theoretical analysis shows that this current reversal is caused by the coupling of the light- and heavy-hole bands and that the hole currents dominate the overall current response. These surprising consequences of band mixing illuminate fundamental physics as they are unique for experiments which are able to monitor electronic transport resulting from carriers with relatively large momenta.}}, author = {{Priyadarshi, S. and Racu, A. M. and Pierz, K. and Siegner, U. and Bieler, M. and Duc, H. T. and Förstner, Jens and Meier, Torsten}}, issn = {{0031-9007}}, journal = {{Physical Review Letters}}, keywords = {{tet_topic_qw}}, number = {{21}}, publisher = {{American Physical Society (APS)}}, title = {{{Reversal of Coherently Controlled Ultrafast Photocurrents by Band Mixing in Undoped GaAs Quantum Wells}}}, doi = {{10.1103/physrevlett.104.217401}}, volume = {{104}}, year = {{2010}}, } @inproceedings{4167, abstract = {{The electromagnetic field in the vicinity of sharp edges needs a special treatment in numeric calculation whenever accurate, fast converging results are necessary. One of the fundamental works concerning field singularities has been proposed in 1972 [1] and states that the electromagnetic energy density must be integrable over any finite domain, even if this domain contains singularities. It is shown, that the magnetic field H(, ϕ) and electric field E(, ϕ) are proportional to ∝ (t−1) for  → 0. The variable  is the distance to the edge and t has to fulfill the integrability condition and thus is restricted to 0 < t < 1. This result is often used to reduce the error corresponding to the singularity without increasing the numerical effort [2 - 5]. For this purpose, a correction factor K is estimated by inserting the proportionality into the wave equation. It is shown, that this method improves the accuracy of the result significantly, however the order of convergence is often not studied. In [4] a method to modify the material parameters in order to use analytic results to improve the numeric calculation is presented. In this contribution we will - inspired by the scheme given in [4] - develop a new method to estimate a correction factor for perfect conducting materials (PEC) and demonstrate the improvement of the results compared to the standard edge correction. Therefore analytic results (comparable to [1]) are consequently merged with the scheme in [4]. The main goal of this work is the calculation of the second harmonic generation (SHG) in the wave response of so-called metamaterials [6]. Frequently these structures contain sharp metallic edges with field singularities at the interfaces which have a strong impact on the SHG signals. Thus, an accurate simulation of singularities is highly important. However, the following approach can also be applied to many other setups, and one of them is shown in the example below.}}, author = {{Classen, C and Förstner, Jens and Meier, Torsten and Schuhmann, R}}, booktitle = {{2010 IEEE Antennas and Propagation Society International Symposium}}, isbn = {{9781424449675}}, keywords = {{tet_topic_numerics}}, location = {{Toronto, ON, Canada}}, publisher = {{IEEE}}, title = {{{Enhanced FDTD edge correction for nonlinear effects calculation}}}, doi = {{10.1109/aps.2010.5562017}}, year = {{2010}}, } @article{4172, abstract = {{Microdisks made from GaAs with embedded InAs quantum dots are immersed in the liquid crystal 4-cyano-4’-pentylbiphenyl (5CB). The quantum dots serve as emitters feeding the optical modes of the photonic cavity. By changing temperature, the liquid crystal undergoes a phase transition from the isotropic to the nematic state, which can be used as an effective tuning mechanism of the photonic modes of the cavity. In the nematic state, the uniaxial electrical anisotropy of the liquid crystal molecules can be exploited for orienting the material in an electric field, thus externally controlling the birefringence of the material. Using this effect, an electric field induced tuning of the modes is achieved. Numerical simulations using the finite-differences time-domain (FDTD) technique employing an anisotropic dielectric medium allow to understand the alignment of the liquid crystal molecules on the surface of the microdisk resonator.}}, author = {{Piegdon, Karoline A. and Declair, Stefan and Förstner, Jens and Meier, Torsten and Matthias, Heiner and Urbanski, Martin and Kitzerow, Heinz-Siegfried and Reuter, Dirk and Wieck, Andreas D. and Lorke, Axel and Meier, Cedrik}}, issn = {{1094-4087}}, journal = {{Optics Express}}, keywords = {{tet_topic_qd, tet_topic_microdisk}}, number = {{8}}, publisher = {{The Optical Society}}, title = {{{Tuning quantum-dot based photonic devices with liquid crystals}}}, doi = {{10.1364/oe.18.007946}}, volume = {{18}}, year = {{2010}}, } @article{1734, author = {{Zentgraf, Thomas and Zhang, Shuang and Oulton, Rupert F. and Zhang, Xiang}}, issn = {{1098-0121}}, journal = {{Physical Review B}}, number = {{19}}, publisher = {{American Physical Society (APS)}}, title = {{{Ultranarrow coupling-induced transparency bands in hybrid plasmonic systems}}}, doi = {{10.1103/physrevb.80.195415}}, volume = {{80}}, year = {{2009}}, } @article{1735, author = {{Oulton, Rupert F. and Sorger, Volker J. and Zentgraf, Thomas and Ma, Ren-Min and Gladden, Christopher and Dai, Lun and Bartal, Guy and Zhang, Xiang}}, issn = {{0028-0836}}, journal = {{Nature}}, number = {{7264}}, pages = {{629--632}}, publisher = {{Springer Nature}}, title = {{{Plasmon lasers at deep subwavelength scale}}}, doi = {{10.1038/nature08364}}, volume = {{461}}, year = {{2009}}, } @article{1736, author = {{Valentine, Jason and Li, Jensen and Zentgraf, Thomas and Bartal, Guy and Zhang, Xiang}}, issn = {{1476-1122}}, journal = {{Nature Materials}}, number = {{7}}, pages = {{568--571}}, publisher = {{Springer Nature}}, title = {{{An optical cloak made of dielectrics}}}, doi = {{10.1038/nmat2461}}, volume = {{8}}, year = {{2009}}, } @article{7973, author = {{Buchholz, S. S. and Fischer, S. F. and Kunze, U. and Reuter, Dirk and Wieck, A. D.}}, issn = {{0003-6951}}, journal = {{Applied Physics Letters}}, number = {{2}}, publisher = {{AIP Publishing}}, title = {{{Nonlocal Aharonov–Bohm conductance oscillations in an asymmetric quantum ring}}}, doi = {{10.1063/1.3069281}}, volume = {{94}}, year = {{2009}}, } @article{4553, abstract = {{We present results on ferroelectric micro-domains obtained by confocal second harmonic microscopy. The high potential of this technique is demonstrated by imaging periodic ferroelectric domain structures in the surface of planar X-cut lithium niobate (LN) and in the body of ridges fabricated by plasma etching on X-cut LN as well. In both cases the measured second harmonic signal reveals a strong contrast between inverted and non-inverted domain sections. This enabled a depth-resolved non-destructive tomography of micro-domains in ridge structures in all three dimensions.}}, author = {{Berth, Gerhard and Wiedemeier, Volker and Hüsch, Klaus-Peter and Gui, Li and Hu, Hui and Sohler, Wolfgang and Zrenner, Artur}}, issn = {{0015-0193}}, journal = {{Ferroelectrics}}, keywords = {{Nonlinear microscopy, ferroelectric micro-domains, confocal imaging, LiNbO3}}, number = {{1}}, pages = {{132--141}}, publisher = {{Informa UK Limited}}, title = {{{Imaging of Ferroelectric Micro-Domains in X-Cut Lithium Niobate by Confocal Second Harmonic Microscopy}}}, doi = {{10.1080/00150190902993267}}, volume = {{389}}, year = {{2009}}, }