@article{43396, abstract = {{A real-space formulation of time-resolved fluorescence of molecular aggregates is developed using the one-exciton density matrix ρ(t) of the optically driven system. A direct relationship is established between the superradiance enhancement factor Ls and the exciton coherence size Lρ associated with the off-diagonal density matrix elements in the molecular representation. Various factors which affect the latter, including finite temperature, energetic disorder, coupling with phonons, and polaron formation are explored. The theory is applied for the interpretation of recent measurements in the B850 system of the LH2 photosynthetic complexes.}}, author = {{Meier, Torsten and Zhao, Y. and Chernyak, V. and Mukamel, S.}}, journal = {{The Journal of chemical physics}}, number = {{10}}, pages = {{3876--3893}}, publisher = {{American Institute of Physics}}, title = {{{Polarons, localization, and excitonic coherence in superradiance of biological antenna complexes}}}, doi = {{10.1063/1.474746}}, volume = {{107}}, year = {{1997}}, } @article{43398, abstract = {{A detailed analysis of the optical and transport properties of semiconductor superlattices in the high-field regime is presented. Electronic Bloch oscillations and the resulting terahertz emission signals are computed including phonon damping in the presence of the electric field. The modifications of the phonon-induced terahertz signal decay are analyzed including the movement of the carriers in the field (intracollisional field effect). For elevated fields it is shown that the interplay between electric field and electron-phonon interaction leads to resonance structures in the terahertz damping rate.}}, author = {{Meier, Torsten and Hader, J. and Koch, M. and Rossi, F. and Linder, N.}}, journal = {{Physical Review B}}, number = {{20}}, pages = {{13799--13807}}, publisher = {{American Physical Society}}, title = {{{Microscopic theory of the intracollisional field effect in semiconductor superlattices}}}, doi = {{10.1103/PhysRevB.55.13799}}, volume = {{55}}, year = {{1997}}, } @article{43397, abstract = {{Two-pulse four-wave-mixing signals from molecular aggregates, including effects of two-exciton states, static disorder, and exciton-phonon interaction represented by arbitrary spectral densities are calculated. Three types of contributions to the signal are identified. The first, reflecting exciton self-correlation, is similar to the photon echo from disordered two-level systems and dominates the signal for long time-delays. The second is related to correlations of one-exciton states, whereas the third reflects correlations between one- and two-exciton states. The information gained by completely resolving the signal field (both amplitude and phase) is analyzed using Wigner spectrograms.}}, author = {{Meier, Torsten and Chernyak, V. and Mukamel, S.}}, journal = {{The Journal of chemical physics}}, number = {{21}}, pages = {{8759--8780}}, publisher = {{American Institute of Physics}}, title = {{{Femtosecond Photon Echoes in Molecular Aggregates}}}, doi = {{10.1063/1.475169}}, volume = {{107}}, year = {{1997}}, } @article{43346, abstract = {{The optical response of CdSe semiconductor nanocrystals is investigated using the reduced single-electron density matrix in real space, calculated by means of the time-dependent Hartree–Fock technique. The spectroscopic signatures of exciton confinement are analyzed using the frequency-dependent electronic coherence matrix (off-diagonal density-matrix elements). The effects of Hartree and the Fock (exchange) type Coulomb interactions on the exciton binding energy are discussed. The latter result in almost dark excitons situated energetically below the main transition. Off-diagonal Coulomb matrix elements lead to larger exciton binding energies compared with previous calculations, and result in a better agreement of the size dependence of the lowest optical transition with experiment.}}, author = {{Meier, Torsten and Yokojima, S. and Mukamel, S.}}, journal = {{The Journal of chemical physics}}, number = {{10}}, pages = {{3837--3853}}, publisher = {{American Institute of Physics}}, title = {{{Density-Matrix-Electronic-Oscillator Representation of Optical Spectroscopy of Semiconductor Nanocrystals}}}, doi = {{10.1063/1.473105}}, volume = {{106}}, year = {{1997}}, } @article{43345, abstract = {{Equations of motion which describe the nonlinear optical response of conjugated polyenes using a collective electronic-oscillator representation are derived. Specific signatures of electronic correlations which enter as anharmonicities and scattering between oscillators are predicted in ultrafast resonant four-wave mixing. Only few resonant oscillators need to be considered explicitly; effects of the remaining (off-resonant) oscillators are introduced via renormalized anharmonic coupling coefficients. The connection with inorganic semiconductors is established.}}, author = {{Meier, Torsten and Tretiak, S. and Chernyak, V. and Mukamel, S.}}, journal = {{Physical Review B}}, number = {{8}}, pages = {{4960--4977}}, publisher = {{American Physical Society}}, title = {{{Electronic-oscillator analysis of femtosecond four-wave mixing in conjugated polyenes}}}, doi = {{10.1103/PhysRevB.55.4960}}, volume = {{55}}, year = {{1997}}, } @inproceedings{44275, abstract = {{The evolution of the quantum mechanical phase of electronic wave packets on seattering-with phonons is an issue of great relevance in solid-state physics. In semiconductor superlattices, evidence for phase conservation on scattering was obtained when time-resolved THz-emission experiments indicated that the dephasing of the probed intraband coherence may proceed slower than the relaxation of carriers via emission of LO-phonons estimated to occur on a 200-fs time scale as in bulk GaAs.1 To corroborate this interpretation, the unknown LO-phonon emission times in the superlattices must be measured for the experimental conditions of the THz-emission experiments. In this paper, a combined investigation of the coherent and incoherent dynamics of optically excited charge carriers in a superlattice structure is presented. A comparison of the characteristic time constants provides clear evidence for the conservation of the phase of the intraband coherence on LO-phonon relaxation.}}, author = {{Meier, Torsten and Wolter, F. and Roskos, H.G. and Je, K.-C and Hader, J. and Rossi, F. and Köhler, K. and Koch, S.W. and Kurz, H.}}, booktitle = {{Quantum Electronics and Laser Science Conference}}, isbn = {{1-55752-501-3}}, location = {{Baltimore, Maryland United States}}, publisher = {{Optical Society of America}}, title = {{{Conservation of intraband coherence upon carrier relaxation by LO-phonon emission}}}, year = {{1997}}, } @inproceedings{44276, abstract = {{In recent years the linear emission dynamics of microcavities containing an optical absorber has been a subject of intense research. For strong coupling between the cavity and the absorber, the spectrum of the coupled system shows two peaks and the linear dynamics of the coupled system is dominated by pronounced oscillations at the normal mode frequency.1 Yet, the uniqueness of the coupled absorber-cavity system cannot be concluded from its linear dynamics.}}, author = {{Meier, Torsten and Koch, M. and Shah, J.}}, booktitle = {{Quantum Electronics and Laser Science Conference}}, isbn = {{1-55752-501-3}}, location = {{Baltimore, Maryland United States}}, publisher = {{Optical Society of America}}, title = {{{Nonlinear dynamics of the coupled exciton-cavity system}}}, year = {{1997}}, } @article{43347, abstract = {{The pump−probe signal from the light-harvesting antenna LH2 of purple bacteria is analyzed using a Green function expression derived by solving the nonlinear exciton-oscillator equations of motion (NEE). A microscopic definition of the exciton mean free path (Lf) and localization size (Lρ) is given in terms of the off-diagonal elements of the exciton Green function and density matrix, respectively. Using phonon-induced (homogeneous) and disorder-induced (inhomogeneous) line widths compatible with superradiane measurements, we find that at 4.2 K the localization size is Lρ = 15 and that the shift ΔΩ between the positive and negative peaks in the differential absorption is determined by a different effective size Lf/2 = 5.6 associated with the exciton mean free path. Our model further predicts the recently observed superradiance coherence size determined by Lρ.}}, author = {{Meier, Torsten and Chernyak, V. and Mukamel, S.}}, journal = {{The Journal of Physical Chemistry B}}, number = {{37}}, pages = {{7332--7342}}, publisher = {{American Chemical Society}}, title = {{{Multiple Exciton Coherence Sizes in Photosynthetic Antenna Complexes viewed by Pump-Probe Spectroscopy}}}, doi = {{10.1021/jp970045v}}, volume = {{101}}, year = {{1997}}, } @inbook{43407, author = {{Meier, Torsten and Koch, S.W. and Stroucken, T. and Knorr, A. and Hader, J. and Rossi, F. and Thomas, P.}}, booktitle = {{Microscopic Theory Of Semiconductors: Quantum Kinetics, Confinement and Lasers}}, editor = {{Koch, S.W.}}, pages = {{81--130}}, publisher = {{World Scientific}}, title = {{{Coherent Dynamics of Semiconductor Heterostructures}}}, doi = {{10.1142/9789812830487_0003}}, year = {{1996}}, } @article{43413, abstract = {{We describe a novel three-pulse degenerate four-wave mixing configuration that permits the direct observation of the coherence between the σ+ and the σ− exciton states in a GaAs quantum well excited in a two-photon process. It is found that the phase coherence between the two single heavy-hole exciton states decays with a time constant that is considerably longer than the dephasing time of the coherence between these states and the ground state (interband coherence). All the experimental data are well described by numerical solutions of the optical Bloch equations for a phenomenological multilevel model.}}, author = {{Meier, Torsten and Bott, K. and Mayer, E.J. and Smith, G.O. and Heuckeroth, V. and Hübner, M. and Kuhl, J. and Schulze, A. and Lindberg, M. and Koch, S.W. and Thomas, P. and Hey, R. and Ploog, K.}}, journal = {{Journal of the Optical Society of America B}}, number = {{5}}, pages = {{1026--1030}}, publisher = {{Optica Publishing Group}}, title = {{{Dephasing of interacting heavy-hole and light-hole excitons in GaAs quantum wells}}}, doi = {{10.1364/JOSAB.13.001026}}, volume = {{13}}, year = {{1996}}, } @inbook{43553, abstract = {{During the last decade, a variety of field-induced coherent phenomena in semiconductor superlattices has received considerable attention both from a theoretical and from an experimental point of view. For the case of a static applied electric field, the existence of Bloch oscillations has been predicted theoretically and confirmed by means of different experimental techniques of nonlinear optical spectroscopy.}}, author = {{Meier, Torsten and Rossi, F. and Je, K.-C and Hader, J. and Thomas, P. and Koch, S.W.}}, booktitle = {{Hot Carriers in Semiconductors}}, editor = {{Hess, K.}}, isbn = {{978-1-4613-8035-1}}, location = {{Chicago}}, pages = {{195--197}}, publisher = {{New York}}, title = {{{On the Observability of dynamic localization in semiconductor superlattices using optical spectroscopy}}}, doi = {{10.1007/978-1-4613-0401-2_46}}, year = {{1996}}, } @inproceedings{43617, author = {{Meier, Torsten and Rossi, F. and Gulia, M. and Selbmann, P.E. and Molinari, E. and Thomas, P. and Thomas, P. and Koch, S.W.}}, booktitle = {{Proceedings of the 23rd ICPS}}, editor = {{Scheffler, M. and Zimmermann, R.}}, location = {{Berlin}}, pages = {{1775--1778}}, publisher = {{World Scientific}}, title = {{{Microscopic theory of the Bloch-oscillation dynamics in semiconductor superlattices: Intra- versus interband Dephasing}}}, year = {{1996}}, } @article{43410, abstract = {{We study exciton ionization induced by an axial electric field in a strongly coupled GaAs/Al0.3Ga0.7 As superlattice at low temperatures. The field-induced ionization times of the heavy-hole 1s exciton in the miniband field regime are determined from transient four-wave-mixing experiments and theoretical model calculations. They are found to decrease with increasing field, and lie in the picosecond and subpicosecond ranges for fields on the order of a few kV/cm. They are considerably longer than those calculated for a 1s exciton in bulk GaAs. We explain this difference as a result of the nonparabolicities in the superlattice miniband dispersion. In addition to studying the field-induced ionization of the 1s resonance, we also investigate the field dependence of excitonic wave packets composed of both bound and continuum states of the exciton. It is found that the continuum components of the wave packet are more sensitive to low electric fields than the 1s component. © 1996 The American Physical Society.}}, author = {{Meier, Torsten and von Plessen, G. and Koch, M. and Feldmann, J. and Thomas, P. and Koch, S.W. and Göbel, E.O. and Goosen, K.W. and Kuo, J.M. and Kopf, R.F.}}, journal = {{Physical Review-Section B-Condensed Matter}}, number = {{20}}, pages = {{13688--13693}}, title = {{{Exciton ionization induced by an electric field in a strongly coupled GaAs/AlxGa1-xAs superlattice}}}, doi = {{10.1103/PhysRevB.53.13688}}, volume = {{53}}, year = {{1996}}, } @article{43416, abstract = {{Beats in the transient four-wave-mixing signal from strongly inhomogeneously broadened semiconductor quantum wells are observed. Based on their phase and polarization properties, the beats are assigned to biexcitons in the mesoscopically disordered material. With increasing excitation intensity a halving of the beat period is observed and is accurately reproduced by calculations including fifth-order contributions.}}, author = {{Meier, Torsten and Albrecht, T.F. and Bott, K. and Schulze, A. and Koch, M. and Cundiff, S.T. and Feldmann, J. and Stolz, W. and Thomas, P. and Koch, S.W. and Göbel, E.O.}}, journal = {{Physical Review B}}, number = {{7}}, pages = {{4436--4439}}, publisher = {{American Physical Society}}, title = {{{Disorder mediated biexcitonic beats in semiconductor quantum wells}}}, doi = {{10.1103/PhysRevB.54.4436}}, volume = {{54}}, year = {{1996}}, } @article{43419, abstract = {{Electronic correlation effects which can be directly probed by ultrafast four-wave mixing are predicted using the electronic-oscillator representation of conjugated polyenes. Comparison with inorganic semiconductors is made possible since the semiconductor Bloch equations projected onto the lowest exciton are obtained as a limiting case. A sign difference in a nonlinear scattering potential clearly shows up in the Wigner spectrogram representing the time and frequency resolved signal.}}, author = {{Meier, Torsten and Mukamel, S.}}, journal = {{Physical review letters}}, number = {{16}}, pages = {{3471--3474}}, publisher = {{American Physical Society}}, title = {{{Femtosecond Spectroscopic Signatures of Electronic Correlations in Conjugated Polyenes and Semiconductor Nanostructures}}}, doi = {{10.1103/PhysRevLett.77.3471}}, volume = {{77}}, year = {{1996}}, } @inbook{43565, abstract = {{The dynamics of carriers induced by electric fields in semiconductor superlattices has received much interest in recent years. Phenomena like Bloch oscillations and negative differential velocity in these structures have been studied using a variety of experimental techniques [1–5]. One particular point of interest has been the transition of the miniband regime to the Bloch oscillation regime with increasing electric field [6,7]. Cw spectra of strongly-coupled superlattices have evidenced that this transition is concomitant with a rapid field-induced ionization of the zero-field miniband exciton [5,8]. While it has been pointed out from the theoretical side that the field-induced ionization process strongly influences the coherent dynamics in the transition region [9], no systematic experimental investigation of the ionization process has been carried out so far. One interesting question that such an investigation could help to answer is to what extent this ionization process differs from the well-documented case of field-induced exciton ionization in bulk semiconductors.}}, author = {{Meier, Torsten and Koch, M. and von Plessen, G. and Feldmann, J. and Koch, S.W. and Thomas, P. and Göbel, E.O. and Goosen, K.W. and Kuo, J.M. and Kopf, R.F.}}, booktitle = {{Hot Carriers in Semiconductors}}, editor = {{Hess, K.}}, isbn = {{10.1007/978-1-4613-0401-2_1}}, location = {{Chicago}}, pages = {{3--6}}, publisher = {{Plenum Press}}, title = {{{Field-induced exciton ionization studied by four-wave mixing}}}, doi = {{10.1007/978-1-4613-0401-2_1}}, year = {{1996}}, } @inbook{43615, author = {{Meier, Torsten and Koch, S.W. and Hader, J. and Je, K.-C and Rossi, F. and Thomas, P.}}, booktitle = {{Frontiers in Nanoscale Science of Micro/Submicro Devices}}, editor = {{Jauho, A.-P. and Buzeaneva, E.V.}}, isbn = {{9780792343011}}, location = {{Kiev}}, pages = {{459--478}}, publisher = {{Kluver Publ.}}, title = {{{Equilibrium and nonequilibrium optical effetcs in semiconductor heterostructures}}}, volume = {{328}}, year = {{1996}}, } @inbook{43559, abstract = {{The progress in the generation of ultrashort laser pulses, together with the development of spectroscopies on this time-scale, has led to a series of experiments which give new insight into the microscopic carrier dynamics in semiconductors. In particular, the energy relaxation of photoexcited carriers has been widely investigated. At the same time, recent progress in the fabrication and characterization of semiconductor heterostructures and superlattices allows a detailed study of a new class of phenomena induced by an applied electric field, such as Bloch oscillations1,2. Both classes of phenomena typically occur on a pico- or femtosecond time-scale, where the coupling between coherent and incoherent phenomena is known to play a dominant role3. Therefore, an adequate theoretical model of the ultrafast dynamics on this time-scale must account for both coherent and incoherent effects on the same kinetic level.}}, author = {{Meier, Torsten and Rossi, F. and Thomas, P. and Koch, S.W. and Selbmann , P.E. and Molinari, E.}}, booktitle = {{Hot Carriers in Semiconductors}}, editor = {{Hess, K.}}, isbn = {{978-1-4613-8035-1}}, location = {{Chicago}}, pages = {{157--160}}, publisher = {{Plenum Press}}, title = {{{Phonon-Induced Suppression of Bloch Oscillations in Semiconductor Superlattices: a Monte Carlo Investigation}}}, doi = {{10.1007/978-1-4613-0401-2_37}}, year = {{1996}}, } @article{43578, abstract = {{Coherent effects are analyzed that are induced by homogeneous electric fields in photoexcited semiconductors. Extended semiconductor Bloch equations are presented, which include the applied electric field, in addition to the many-body Coulomb contributions in the time-dependent Hartree-Fock approximation. These equations are solved for a one-dimensional tight-binding model of a semiconductor superlattice. Linear and nonlinear optical signals associated with the coherent field-induced effects are calculated. For the case of a static electric field, the influence of the Coulomb interaction, which is treated on the Hartree-Fock level for a contact potential approximation, on the Bloch oscillations, and on their counterpart in the frequency domain, the Wannier-Stark-ladder, is analyzed. For a time-dependent electric field, dynamic localization, i.e., the localization of electrons due to an oscillating electric field, is analyzed. It is predicted that the dynamic localization should be observable in semiconductor superlattices even in the presence of Coulomb interaction.}}, author = {{Meier, Torsten and von Plessen, G. and Thomas, P. and Koch, S.W.}}, journal = {{Physical Review B}}, number = {{20}}, pages = {{14490--14497}}, publisher = {{American Physical Society}}, title = {{{Coherent effects induced by static and time-dependent electric fields in semiconductors}}}, doi = {{10.1103/PhysRevB.51.14490}}, volume = {{51}}, year = {{1995}}, } @article{43586, abstract = {{We report results on selection rules and polarization conditions for quantum beating between light hole and heavy hole excitons in GaAs quantum wells. The measurements were conducted using time-integrated degenerate-four-wave-mixing in a three-pulse configuration. By choosing particular polarization configurations of the ultrashort optical pulses exciting heavy and light hole excitons simultaneously, degenerate four-wave-mixing signals show either quantum beating or no modulation at all. The experiments are analyzed using a model that takes into account exciton/exciton interaction.}}, author = {{Meier, Torsten and Smith, G.O. and Mayer, E.J. and Heuckeroth, V. and Kuhl, J. and Bott, K. and Schulze, A. and Bennhardt, D. and Koch, S.W. and Thomas, P. and Hey, R. and Ploog, K.}}, journal = {{Solid state communications}}, number = {{5}}, pages = {{373--377}}, publisher = {{Pergamon}}, title = {{{Polarization selection rules for quantum beating between light-and heavy-hole excitons in GaAs quantum wells}}}, doi = {{10.1016/0038-1098(95)00052-6}}, volume = {{94}}, year = {{1995}}, }