@article{43340, abstract = {{Femtosecond two beam and three beam ( ω1,ω1;ω2) four-wave mixing (FWM) experiments on GaAs quantum wells have been performed using two partially synchronized, independently tunable lasers with external jitter compensation. Heavy and light hole beatings are observed with these two mutually incoherent lasers. FWM signals are observed when ω2 is completely below the exciton energies, with no spectral overlap with the absorption profile. These off-resonant signals are stronger than the interband continuum signals for equivalent detunings.}}, author = {{Meier, Torsten and Kim, D.S. and Sohn, J.Y. and Yahng, J.S. and Ahn, Y. H. and Yee, K.J. and Yee, D.S. and Cho, Y.D. and Hong, S.C. and Kim, W.S. and Woo, J.C. and Koch, S.W. and Woo, D.H. and Kim, E. K. and Kim , S.H. and Kim, C.S.}}, journal = {{Physical review letters}}, number = {{21}}, pages = {{4803--4806}}, publisher = {{American Physical Society}}, title = {{{Femtosecond four-wave mixing experiments on GaAs quantum wells using two independently tunable lasers}}}, doi = {{10.1103/PhysRevLett.80.4803}}, volume = {{80}}, year = {{1998}}, } @article{43341, abstract = {{Closed Green-function expressions for the third-order response of semiconductors are derived by mapping the two-band model onto the much simpler molecular (Frenkel) Hamiltonian. The signatures of two-exciton resonances are incorporated through the exciton scattering matrix, totally avoiding the explicit calculation of two-exciton states. Exact expressions for the nonlinear optical response of two-dimensional semiconductor nanostructures in a strong perpendicular magnetic field are derived by truncating at the n=1 Landau level, and using the symmetry of the system and a group-theoretical analysis. We find that the nonlinear optical response depends crucially on asymmetries between particle-particle and particle-hole Coulomb interactions.}}, author = {{Meier, Torsten and Chernyak, V. and Yokojima, S. and Mukamel, S.}}, journal = {{Physical Review B}}, number = {{8}}, pages = {{4496--4516}}, publisher = {{American Physical Society}}, title = {{{Effective Frenkel Hamiltonian for optical nonlinearities in semiconductors: Application to magnetoexcitons}}}, doi = {{10.1103/PhysRevB.58.4496}}, volume = {{58}}, year = {{1998}}, } @article{43343, abstract = {{In his Comment on our work Glutsch raises, on the basis of a calculation for a dimerized three-dimensional superlattice, four points: (1) odd-parity excitons do not contribute to optical absorption, (2) there are no forbidden single-particle transitions, (3) there is a coupling of the e1-hh2 exciton (called ¯X in Ref. 1) to the underlying e1-hh1 continuum that leads to a Fano resonance, and (4) the extension of the exciton wave function is infinite in an all space directions rather than having a small extension. In this Reply these four points are addressed and it is shown that our previous conclusions remain valid.}}, author = {{Meier, Torsten and Bott, K. and Hader, J. and Brinkmann, D. and Koch, S.W. and Thomas, P.}}, journal = {{Physical Review B}}, number = {{23}}, publisher = {{American Physical Society}}, title = {{{Reply to Comment on "Odd-parity excitons in semiconductor superlattices"}}}, doi = {{10.1103/PhysRevB.58.15911}}, volume = {{58}}, year = {{1998}}, } @article{43344, abstract = {{Absorption and differential electroabsorption spectra of a GaInAs/InP superlattice in the regime of Wannier–Stark localization are compared with spectra derived from the Semiconductors Bloch Equations. The absorption is strongly underestimated for higher energies by the effective mass approximation but good agreement is achieved by using an energy dependent in-plane effective mass. No fitting parameters are used except for a phenomenological broadening. The lineshape of the field-modulated spectra is dominated by the strong field dependence of Wannier–Stark transitions and depends on the amplitude of the modulating field which should be kept small for best results. REFERENCES}}, author = {{Meier, Torsten and Thränhardt, A. and Kolbe, H.J. and Hader, J. and Weiser, G. and Koch, S.W.}}, journal = {{Applied Physics Letters}}, number = {{18}}, pages = {{2612--2614}}, publisher = {{American Institute of Physics}}, title = {{{Field-dependent absorption in superlattices: Comparison of theory and experiment}}}, doi = {{10.1063/1.122522}}, volume = {{73}}, year = {{1998}}, } @article{43342, abstract = {{The four-wave mixing (FWM) signal of a semiconductor superlattice with an external electric field is evaluated using the semiconductor Bloch equations. It is found that the FWM signal for a GaAs/AlGaAs-semiconductor superlattices with a lattice constant d has a deep valley when the electric field is around eF d = 1 meV. It is also found that the deep valley comes mainly from the broken inversion symmetry caused by the exteral electric field and that the field intensity determines the sign and the magnitude of the Coulomb-induced optical nonlinearities.}}, author = {{Meier, Torsten and Je, K.-C and Kim, Y. and Koch, S.W.}}, journal = {{Journal of the Korean Physical Society}}, number = {{4}}, pages = {{437--440}}, title = {{{Field-Induced Four-Wave Mixing Signal in Semiconductor Superlattices}}}, volume = {{32}}, year = {{1998}}, } @inproceedings{44274, abstract = {{Femtosecond four-wave mixing experiments on GaAs/AlGaAs quantum wells are performed with two independently tunable lasers. Many new results are found, including the heavy-hole-light-hole beating with these two mutually incoherent lasers.}}, author = {{Meier, Torsten and Yahng, J.S. and Ahn, Y. H. and Sohn, J.Y. and Koch, S.W. and Kim, D.S.}}, booktitle = {{Ultrafast Phenomena XI}}, isbn = {{10.1007/978-3-642-72289-9_70}}, location = {{Garmisch-Partenkirchen, Germany}}, pages = {{236--238}}, publisher = {{Springer, Berlin, Heidelberg}}, title = {{{Femtosecond Two Color Four-Wave Mixing Experiments on GaAs Quantum Wells Using Two Independently Tunable Lasers}}}, doi = {{10.1007/978-3-642-72289-9_70}}, year = {{1998}}, } @article{13773, author = {{Schmidt, Wolf Gero and Bechstedt, F. and Esser, N. and Pristovsek, M. and Schultz, Ch. and Richter, W.}}, issn = {{0163-1829}}, journal = {{Physical Review B}}, number = {{23}}, pages = {{14596--14599}}, title = {{{Atomic structure of InP(001)-(2×4): A dimer reconstruction}}}, doi = {{10.1103/physrevb.57.14596}}, volume = {{57}}, year = {{1998}}, } @article{13772, author = {{Schmidt, Wolf Gero and Bechstedt, F.}}, issn = {{0039-6028}}, journal = {{Surface Science}}, number = {{3}}, pages = {{474--484}}, title = {{{Geometry and electronic structure of InP(001)(2×4) reconstructions}}}, doi = {{10.1016/s0039-6028(98)00260-x}}, volume = {{409}}, year = {{1998}}, } @article{13771, author = {{Shkrebtii, A. I. and Esser, N. and Richter, W. and Schmidt, Wolf Gero and Bechstedt, F. and Fimland, B. O. and Kley, A. and Del Sole, R.}}, issn = {{0031-9007}}, journal = {{Physical Review Letters}}, number = {{3}}, pages = {{721--724}}, title = {{{Reflectance Anisotropy of GaAs(100): Theory and Experiment}}}, doi = {{10.1103/physrevlett.81.721}}, volume = {{81}}, year = {{1998}}, } @article{13774, author = {{Schmidt, Wolf Gero and Käckell, P. and Bechstedt, F.}}, issn = {{0169-4332}}, journal = {{Applied Surface Science}}, pages = {{136--140}}, title = {{{In-induced (4 × 2) reconstructions of GaAs(001) surfaces}}}, doi = {{10.1016/s0169-4332(97)00510-2}}, volume = {{123-124}}, year = {{1998}}, } @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}}, } @article{13775, author = {{Schmidt, Wolf Gero}}, issn = {{0947-8396}}, journal = {{Applied Physics A: Materials Science & Processing}}, pages = {{581--586}}, title = {{{(4×2) and (2×4) reconstructions of GaAs and InP(001) surfaces}}}, doi = {{10.1007/s003390050625}}, volume = {{65}}, year = {{1997}}, } @article{13776, author = {{Nilen, R W N and Connell, S H and Britton, D T and Fischer, C G and Sendezera, E J and Schaaff, P and Schmidt, Wolf Gero and Sellschop, J P F and Verwoerd, W S}}, issn = {{0953-8984}}, journal = {{Journal of Physics: Condensed Matter}}, pages = {{6323--6333}}, title = {{{The anisotropic electron - positron momentum distribution in diamond}}}, doi = {{10.1088/0953-8984/9/29/017}}, volume = {{9}}, year = {{1997}}, }