@article{43596, author = {{Meier, Torsten and von Plessen, G. and Feldmann, J. and Thomas, P. and Göbel, E.O. and Koch, S.W.}}, journal = {{Optics and Photonics News}}, number = {{12}}, pages = {{20--21}}, publisher = {{Optical Society of America}}, title = {{{Intrinsic perturbations of Bloch oscillations and Wannier Stark ladders in semiconductor superlattices}}}, doi = {{10.1364/OPN.5.12.000020}}, volume = {{5}}, year = {{1994}}, } @inproceedings{44283, abstract = {{The strong influence of exciton/exciton interaction on the nonlinear optical response of the 2D exciton in GaAs quantum wells has been demonstrated in several recent experimental studies. The theoretical model for the microscopic coupling mechanism is still the subject of controversy, however. In ref. [1], we have presented a model including a density dependent coupling between opposite spin excitons which assumes that the interaction results in a renormalization of the matrix elements, dephasing rates and energies of the transition from the single-exciton state to the two-exciton state with respect to the corresponding quantities for the single exciton transitions. In contrast, Wang et al. claim that all experimental observations are explained by a density induced dephasing rate and that biexciton states play no role [2]. Here we present a new 3-pulse degenerate-four-wave-mixing (DFWM) configuration which is able to differentiate between pure local field effects and biexcitonic contributions to the time-integrated signal. Experiments were performed on an almost homogeneously broadened GaAs/Al0.3Ga0.7As single QW (well width 20 nm, photoluminescence line 0.3 meV, homogenous linewidth 0.15 meV) in the backward reflection geometry. The sample was cooled to 10 K and excited by a sequence of three pulses (1.1 ps duration) with equal intensity, wave vectors 𝑘→1,𝑘→2,𝑘→3 and delays τ12 and τ13 between the second and first and the third and first pulse, respectively. The signal was monitored in the direction 𝑘→𝑠=𝑘→1+𝑘→2−𝑘→3 which provides no signal for the chosen pulse length if local field and renormalization effects are negligible. The peak intensity of the time-integrated DFWM signal has been calculated by solving the optical Bloch for a system of two non-interacting two-level systems (2LS) with opposite circular polarization selection rules (local field effect) and for the renormalized four-level system (4LS) depicted in Fig. 1 which assumes the formation of biexcitons between excitons with opposite spins. The signal strength is proportional to the strength of the local field in the case of the 2LS and to the renormalization for the 4LS. The peak signal intensities expected for pure local field and pure biexction contributions are summarized in the second and third column of Table 1 for eight experimental configurations applying different linear and circularly polarized pulses. The values are normalized to the signal strength predicted for three parallel linearly polarized pulses. Close inspection of the data reveals remarkable differences of the peak amplitude with polarization geometry for the two coupling models.}}, author = {{Meier, Torsten and Kuhl, J. and Mayer, E.J. and Smith, G.O. and Bennhardt, D. and Schulze, A. and Thomas, P. and Hey, R. and Ploog, K.}}, booktitle = {{International Conference on Ultrafast Phenomena}}, location = {{California, United States}}, title = {{{Contributions of Bound and Unbound Two-Exciton States to the Nonlinear Optical Response of GaAs Quantum Wells}}}, doi = {{10.1364/UP.1994.MD.5}}, year = {{1994}}, } @inproceedings{44284, abstract = {{Several recent experimental and theoretical studies have demonstrated the importance of exciton/exciton coupling due to Coulomb interactions for the nonlinear optical response of the 2D exciton in GaAs quantum wells (QWs).1,2 These results imply that multilevel models are required in order to provide a theoretically appropriate description of the nonlinear behavior. Previous application of a renormalized 9-level system has proven successful in describing the third-order response of hh-excitons in GaAs quantum wells.2 We present a comprehensive experimental and theoretical investigation of the polarization selection rules for degenerate- four-wave-mixing (DFWM) and quantum beating of hh and lh transitions in a GaAs QW. Depending on the polarization and temporal sequence of the three pulses simultaneous excitation of the hh and lh transitions generates either quantum beats (QB), no modulation of the signal, or a superposition of QB and polarization interference (PI) effects as proved by spectrally resolved (SR)-DFWM.}}, author = {{Meier, Torsten and Mayer, E.J. and Smith, G.O. and Kuhl, J. and Schulze, A. and Bennhardt, D. and Koch, S.W. and Thomas, P. and Hey, R. and Ploog, K.}}, booktitle = {{Proceedings of the 5th European Quantum Electronics Conference}}, location = {{Amsterdam, Netherlands}}, pages = {{187--188}}, title = {{{Polarization selection rules for quantum beating between light and heavy holes in GaAs quantum wells}}}, year = {{1994}}, } @inproceedings{44282, abstract = {{Although the importance of exciton/exciton interactions for the nonlinear optical response of GaAs quantum wells (QW) is well established by many experimental observations, the role of biexciton states in these processes is still an open question, even at low excitation densities. Evidence for the formation of biexcitons has been independently derived from pump-probe studies [1], from the density dependence of the photoluminescence (PL) line shape [2] and from signal modulations observed in degenerate-four-wave-mixing (DFWM) with incoherent light pulses [3]. Here, we report on time-resolved DFWM with parallel (PP) and cross-polarized (CP) pulses. Depending on the polarization geometry, the signals reveal strong quantum beats which correspond to the splitting between either the heavy hole (hh) and light hole (lh) exciton or the hh exciton and the biexciton.}}, author = {{Meier, Torsten and Mayer, E.J. and Smith, G.O. and Kuhl, J. and Bennhardt, D. and Schulze, A. and Thomas, P. and Hey, R. and Ploog, K.}}, booktitle = {{International Conference on Ultrafast Phenomena}}, location = {{California, United States}}, title = {{{Observation of Biexcitons in Time-Resolved Degenerate-Four-Wave-Mixing on GaAs Quantum Wells}}}, year = {{1994}}, } @inproceedings{43600, abstract = {{We have performed sub-picosecond four-wave mixing experiments on a series of symmetrically strained (GaIn)As/Ga(AsP) multiple quantum wells. We show that these measurements allow a precise determination of exciton binding energies. One of the advantages of this quantum beat method as compared to linear optical methods is that a determination of the exciton binding energy is possible even in the presence of considerable inhomogeneous broadening. In addition, the dependence of the exciton binding energy on the strain in the (GaIn)As quantum well layers suggests that the reduced electron-hole effective mass is not influenced by the increase in strain.}}, author = {{Meier, Torsten and Koch, M. and Stolz, W. and Feldmann, J. and Thomas, P. and Göbel, E.O.}}, booktitle = {{Proceedings der 7. International Conference on Superlattices, Microstructures and Microdevices}}, location = {{Banff, Canada}}, number = {{3}}, pages = {{329--332}}, title = {{{Determination of excitonic binding energies in symmetrically strained (GaIn)As/Ga(PAs) multiple quantum wells using quantum beat spectroscopy}}}, doi = {{10.1006/spmi.1994.1064}}, volume = {{15}}, year = {{1994}}, } @inproceedings{44280, abstract = {{In the absence of scattering mechanisms, a crystal electron subjected to a homogeneous electric field undergoes a periodic motion in both momentum and real space. This oscillatory motion is known as Bloch oscillations (BOs) and has recently been detected in transient four-wave mixing (FWM) and Tera-Hertz emission experiments on semiconductor superlattices. It is generally assumed that the minimum field required for the observation of BOs is controlled by the rate of scattering in the material. However, an experimental verification of this point is still lacking.}}, author = {{Meier, Torsten and von Plessen, G. and Feldmann, J. and Göbel, E.O. and Thomas, P. and Goossen, K.W. and Kuo, J.M. and Kopf, R.F.}}, booktitle = {{International Quantum Electronics Conference}}, isbn = {{1-55752-342-8}}, location = {{Anaheim, California United States}}, title = {{{Field-induced dynamics of a wave packet in a wide superlattice miniband}}}, year = {{1994}}, } @inproceedings{44279, abstract = {{The strong nonlinear optical response of the 2D exciton in GaAs quantum wells at relatively low excitation densities has been observed in many experimental studies in accordance with theoretical predictions. In principle, exciton/exciton interaction results in a renormalization of the transition matrix elements, dephasing rates and frequencies of the excitonic states. Wang et al.1 claimed that all experimental results can be explained by a density- induced enhanced dephasing rate. In a previous paper,2 we have suggested a density dependent coupling between opposite spin excitons, which involves all three renormalization phenomena.}}, author = {{Meier, Torsten and Smith, G.O. and Mayer, E.J. and Kuhl, J. and Schulze, A. and Bennhardt, D. and Koch, S.W. and Thomas, P. and Hey, R. and Ploog, K.}}, booktitle = {{European Quantum Electronics Conference}}, location = {{Amsterdam, Netherlands}}, title = {{{Direct verification of the existence of biexcitons in GaAs qauntum wells}}}, year = {{1994}}, } @inproceedings{44285, abstract = {{A proper description of subpicosecond four-wave-mixing (FWM) experiments for excitonic transitions in semiconductor heterostructures must consider the fact that the spectrally broad laser pulses excite not only the 1s bound exciton state but also energetically higher bound exciton states and the lower-lying part of the unbound continuum states. In this paper, we report results of transient and time-resolved FWM-experiments in which such ’excitonic wave packets’ play a crucial role. In addition, a theoretical treatment of the problem based on the solution of the semiconductor Bloch is presented. We show that the time-dependent nonlinear response is determined by an interplay between inhomogeneous broadening and Coulomb interaction.}}, author = {{Meier, Torsten and Koch, M. and Jahnke, F. and Feldmann, J. and Schäfer, W. and Thomas, P. and Koch, S.W. and Göbel, E.O. and Nickel, H.}}, location = {{California, United States}}, title = {{{Interplay Between Inhomogeneous Broadening and Coulomb Interaction in the Dynamics of Excitonic Wave Packets}}}, doi = {{10.1364/UP.1994.TuE.3}}, year = {{1994}}, } @article{13856, author = {{Schmidt, Wolf Gero and Wenzien, B. and Bechstedt, F.}}, issn = {{0163-1829}}, journal = {{Physical Review B}}, number = {{7}}, pages = {{4731--4744}}, title = {{{Chemisorption of antimony on GaAs(110)}}}, doi = {{10.1103/physrevb.49.4731}}, volume = {{49}}, year = {{1994}}, } @article{13855, author = {{Schmidt, Wolf Gero and Wenzien, Bernd and Bechstedt, Friedhelm}}, issn = {{0039-6028}}, journal = {{Surface Science}}, number = {{Part A}}, pages = {{235--240}}, title = {{{Coverage-dependent bonding of Sb on GaAs (110)}}}, doi = {{10.1016/0039-6028(94)90400-6}}, volume = {{307-309}}, year = {{1994}}, } @article{13853, author = {{Bechstedt, F and Schmidt, Wolf Gero and Wenzien, B}}, issn = {{0295-5075}}, journal = {{Europhysics Letters (EPL)}}, number = {{5}}, pages = {{357--362}}, title = {{{Energetics and Structure of Ordered Sb Overlayers and Sb Clusters on GaAs(110) Probed by Ab Initio Calculations}}}, doi = {{10.1209/0295-5075/25/5/008}}, volume = {{25}}, year = {{1994}}, } @article{13854, author = {{Schmidt, Wolf Gero and Srivastava, GP}}, issn = {{0038-1098}}, journal = {{Solid State Communications}}, number = {{4}}, pages = {{345--348}}, title = {{{First principles calculations of interface phonons of an Epitaxial Sb monolayer on GaAs(110) and InP(110)}}}, doi = {{10.1016/0038-1098(94)90597-5}}, volume = {{89}}, year = {{1994}}, } @article{43449, abstract = {{We present subpicosecond time-resolved four-wave-mixing studies on GaAs/AlAs short-period superlattices having different miniband widths. Photon echoes are observed as a consequence of the inhomogeneous broadening of the excitonic resonance. In addition, the photon-echo signal exhibits periodic modulations as a function of the time delay between the excitation laser pulses. Free excitons and excitons bound to neutral acceptors are identified as the underlying three-level system leading to the observed photon-echo quantum beats. From the beat period we can directly infer the dissociation energy of the bound exciton. In accordance with theory, we find that the dissociation energy decreases with increasing miniband width, i.e., when the excitons become less confined. In addition, we find that the dephasing rate of bound excitons is about one order of magnitude less than that of free excitons and is mainly determined by energy relaxation.}}, author = {{Meier, Torsten and Koch, M. and Weber, D. and Feldmann, J. and Göbel, E.O. and Schulze, A. and Thomas, P. and Schmitt-Rink, S. and Ploog, K.}}, journal = {{Physical Review B}}, number = {{3}}, pages = {{1532--1539}}, publisher = {{American Physical Society}}, title = {{{Subpicosecond photon-echo spectroscopy on GaAs/AlAs short-period superlattices}}}, doi = {{10.1103/PhysRevB.47.1532}}, volume = {{47}}, year = {{1993}}, } @inbook{43442, abstract = {{Femtosecond nonlinear laser spectroscopy is applied to study the dynamics of coherent optical excitations in semiconductors. In particular, beat phenomena of excitonic excitations in quantum wells and superlattice structures will be considered. We will demonstrate that four wave mixing experiments with time resolved detection of the nonlinear signal are able to distinguish between quantum beats and polarization interference. In addition, we report for a GaAs/AlAs superlattice the observation of quantum beats in the photon echo signal. The occurence of these beats is attributed to the simultaneous excitation of bound and localized excitons.}}, author = {{Meier, Torsten and Göbel, E.O. and Koch, M. and Feldmann, J. and von Plessen, G. and Schulze, A. and Thomas, P. and Schmitt-Rink, S. and Köhler, K. and Ploog, K.}}, booktitle = {{Optical Phenomena in Semiconductor Structures of Reduced Dimension}}, editor = {{Lookwood, D. and Pinczuk, A.}}, isbn = {{978-94-010-4845-3}}, pages = {{145--155}}, publisher = {{Springer}}, title = {{{Time resolved Four Wave Mixing in GaAs/AlAs Quantum Well Structures}}}, doi = {{10.1007/978-94-011-1912-2_14}}, year = {{1993}}, } @article{43448, abstract = {{We report on the coherent dynamics of excitonic wave packets observed in transient four-wave mixing experiments on strained InGaAs/GaAs quantum-well structures. The excitonic noneigenstates are created by using laser pulses shorter than the electron round trip time within the exciton orbital. A characteristic temporal modulation of the diffracted signal is observed, which resembles the coherent dynamics of an electron wave packet in a hydrogen atom expected for the case of a simultaneous excitation of all bound and the lowest continuum states.}}, author = {{Meier, Torsten and Feldmann, J. and von Plessen, G. and Koch, M. and Göbel, E.O. and Thomas, P. and Bacher, G. and Hartmann, C. and Schweizer, H. and Schäfer, W. and Nickel, H.}}, journal = {{Physical review letters}}, number = {{20}}, pages = {{3027--3030}}, publisher = {{American Physical Society}}, title = {{{Coherent Dynamics of Excitonic Wave Packets}}}, doi = {{10.1103/PhysRevLett.70.3027}}, volume = {{70}}, year = {{1993}}, } @article{43447, abstract = {{Exciton coupling is studied for double quantum wells, which are separated by thick barriers. Results are presented for the linear optical spectrum, stationary and transient luminescence as well as four-wave-mixing signals. Additionally, coherent and incoherent transport through the barrier is considered}}, author = {{Meier, Torsten and Batsch, M. and Thomas, P. and Lindberg, M. and Koch, S.W. and Shah, J.}}, journal = {{Physical Review B}}, number = {{16}}, pages = {{11817--11826}}, publisher = {{American Physical Society}}, title = {{{Dipole-dipole coupling of excitons in double quantum wells}}}, doi = {{10.1103/PhysRevB.48.11817}}, volume = {{48}}, year = {{1993}}, } @inproceedings{44286, abstract = {{In degenerate four-wave-mixing (DFWM) experiments the polarization of the incident laser pulses can have a strong influence on the measured signal. For GaAs quantum wells a number of DFWM experiments were performed by using either parallel or perpendicular polarization of the incident laser pulses. Experimentally, it turned out that some characteristic features of the signal differ appreciably for the two configurations. In particular, different dephasing times, phase shifts of the quantum beats, different time-resolved behavior (echoes versus free-induction decay), and intensity dependence of the measured signal have been reported}}, author = {{Meier, Torsten and Bennhardt, D. and Thomas, P. and Eccleston, R. and Mayer, E. and Kuhl, J.}}, booktitle = {{Quantum Electronics and Laser Science Conference}}, isbn = {{1-55752-302-9}}, location = {{Baltimore, Maryland United States}}, title = {{{Theory for polarization-dependent four-wave-mixing signals in quantum wells}}}, year = {{1993}}, } @inproceedings{44287, abstract = {{We investigate the coherent coupling of free and bound excitonic transitions, as wets as of distinct excitonic transitions arising from spatially separated quantum-well islands by means of time-resolved four-wave-mixing experiments.}}, author = {{Meier, Torsten and Koch, M. and Feldmann, J. and von Plessen, G. and Schulze, A. and Göbel, E.O. and Thomas, P. and Schmitt-Rink, S. and Shah, J. and Ploog, K. and Köhler, K.}}, booktitle = {{Quantum Electronics and Laser Science Conference}}, isbn = {{1-55752-302-9}}, location = {{Baltimore, Maryland United States}}, title = {{{Coherent coupling of exciton transitions in semiconductor quantum structures}}}, year = {{1993}}, } @article{13858, author = {{Schmidt, Wolf Gero and Wenzien, Bernd and Bechstedt, Friedhelm}}, issn = {{0011-4626}}, journal = {{Czechoslovak Journal of Physics}}, number = {{9-10}}, pages = {{1003--1007}}, title = {{{AB initio calculation of the atomic and electronic structure for Sb adsorbed on GaAs(110)}}}, doi = {{10.1007/bf01595293}}, volume = {{43}}, year = {{1993}}, } @article{13857, author = {{Schmidt, Wolf Gero and Srivastava, G P}}, issn = {{0953-8984}}, journal = {{Journal of Physics: Condensed Matter}}, number = {{49}}, pages = {{9025--9036}}, title = {{{Chemisorption of aluminium on GaAs(110)}}}, doi = {{10.1088/0953-8984/5/49/005}}, volume = {{5}}, year = {{1993}}, }