bluuebunny/crossref_metadata_2025_split huggingface dataset:
Density‐matrix description of frequency‐resolved secondary emission from quantum wells
Authors: Mannarini Gianandrea , Zimmermann Roland , Kocherscheidt Gerrit , Langbein Wolfgang 
Published: July 2003

AbstractThe frequency‐resolved secondary emission from excitons in a single 8 nm‐wide quantum well is investigated using speckle analysis. We model these experiments starting with a Hamiltonian in the basis of disorder eigenstates of excitons, interacting both with light and acoustical phonons. The distinction between incoherent and coherent secondary emission is intimately related with the decomposition of a two‐time exciton density‐matrix into a diagonal, incoherent part and a product of polarizations. The latter gives rise to speckling (intensity variations over observation angle), and is called resonant Rayleigh scattering. The results of our simulation agree pretty well with the experimental data and allow a determination of the coherent and incoherent exciton distributions.
Autocorrelation spectroscopy on single GaInAs/GaAs quantum wells
Authors: Neuberth Ulrich , von Freymann Georg , Wegener Martin , Nau Siegfried , Stolz Wolfgang 
Published: July 2003

AbstractWe investigate an atomically rough single GaInAs/GaAs quantum well by means of autocorrelation spectroscopy. The data are based on thousands of individual low‐temperature nano‐photoluminescence spectra and exhibit a peak around 1.8 meV energy difference. On the same sample, we measure the topography of one of the buried heterointerfaces which is possible by using highly‐selective etching and atomic force microscopy.
Ultrafast dephasing in strongly correlated systems
Authors: Perakis I. E. 
Published: July 2003

AbstractUsing projection techniques we derive the equation of motion for the third‐order nonlinear optical polarization of a strongly correlated system. We do not assume a Hartree–Fock ground state, but include the ground state correlations via time‐independent interaction parameters and energies. Our theory can be used to describe the ultrafast nonlinear optical response of a strongly correlated cold electron gas, such as the two‐dimensional electron gas in the quantum Hall effect regime. For this system, we show that the collective electronic excitations lead to a time‐dependent coupling of the Landau level magnetoexcitons and a strong non‐Markovian exciton dephasing. We discuss the signatures in the transient four‐wave‐mixing spectrum.
Phase diagram of the quantum degenerate electron–hole system in diamond
Authors: Nagai Masaya , Shimano Ryo , Horiuch Kenji , Kuwata‐Gonokami Makoto 
Published: July 2003

AbstractWe measured the emission spectra under strong excitation above the band gap using femtosecond pulses and observed the exciton Mott transition at high temperature and the liquid–gas transition below 160 K from temperature and excitation density dependences of emission spectra. From these results we determined the phase diagram of electron–hole system in diamond.
Nonlinear optical dynamics of excitons and trions
Authors: Portella‐Oberli M. T. , Ciulin V. , Kutrowski M. , Wojtowicz T. , Deveaud B. 
Published: July 2003

AbstractWe investigate the nonlinear optical dynamics of excitons and trions in CdTe modulation‐doped quantum wells by time and spectrally resolved pump–probe experiments. We find that the nonlinearities induced by excitons are different from those due to the presence of the trions. From a comparison between the exciton and trion behaviours, we show that, at low temperature, trions are formed from excitons in about 10 picoseconds and, as the temperature is increased, a thermal equilibrium is reached between exciton and trion populations within 5 picoseconds.
Coherent control of carrier population and spin in (111)‐GaAs
Authors: Stevens Martin J. , Bhat R. D. R. , Sipe J. E. , van Driel H. M. , Smirl Arthur L. 
Published: July 2003

AbstractWe report independent coherent control of carrier population and spin in (111)‐oriented GaAs arising through quantum interference of the transition amplitudes associated with one‐ and two‐photon absorption of ∼100 fs phase‐locked optical pulses. We demonstrate this coherent control using various combinations of pulse polarizations and crystal orientations. In addition, we present a phenomenological framework for the spin and population control, and present predictions based on a macroscopic symmetry analysis that agree with our experimental observations.
Analytical results for nonlinear optical signals from quantum dots coupled to phonons
Authors: Axt V. M. , Krummheuer B. , Vagov A. , Kuhn T. 
Published: July 2003

AbstractThe impact of pure dephasing processes on the optically induced nonlinear dynamics of quantum dots is analyzed. Concentrating on small dots pure dephasing can be studied analytically in the limit of ultrafast excitation. General conclusions from the analysis of the closed form formulas include the prediction that four‐wave‐mixing (FWM) spectra of single dots change from asymmetric to symmetric lineshapes with increasing pulse delay. Furthermore, in contrast to phenomenological dephasing models the delay dependence of the time integrated FWM amplitude |PFWM| generated by a strongly inhomogeneously broadened ensemble deviates from the real time dependence of |Plin|2, where Plin is the linear polarization emitted by a single dot. Numerical results are presented for FWM signals from dots coupled to bulk acoustic phonons. Surprisingly, the initial decay time of the signal depends non‐monotonously on the temperature. In addition, it is shown that for certain material parameters the coupling to the smooth continuum of acoustic phonons may result in pronounced oscillations.
Influence of coupling between localized and continuum states in InGaN quantum‐dot systems
Authors: Schneider H. C. , Chow W. W. , Koch S. W. 
Published: July 2003

AbstractThis paper investigates the influence of the coupling between localized and continuum states on the optical absorption in wide‐bandgap nitride‐based quantum‐dot structures under high‐excitation conditions. Calculating the optical susceptibility in the presence of strong many‐body Coulomb interactions and the quantum‐confined Stark effect, we show that the interplay of these effects results in absorption/gain features that depend on the quantum‐dot dimensions in a nontrivial way.
Dephasing of biexcitons in InGaAs quantum dots
Authors: Borri P. , Langbein W. , Schneider S. , Woggon U. , Sellin R. L. , Ouyang D. , Bimberg D. 
Published: July 2003

AbstractWe present measurements of the dephasing time of biexcitonic transitions in self‐organized InGaAs quantum dots in the temperature range from 10 K to 70 K. We use an heterodyne four‐wave mixing technique that allows direct measurement of the dephasing time in an inhomogeneously broadened quantum‐dot ensemble. By applying an electrical injection, we progressively increase the number of carriers in the quantum dots and investigate the passage from a four‐wave mixing response dominated by the one‐exciton transition to a response dominated by biexcitonic and multiexcitonic transitions. The temperature dependence of the homogeneous broadening of the biexciton‐to‐exciton transition is extrapolated to zero injection current and its physical origin in terms of radiative recombination and phonon interactions is discussed.
Nonequilibrium theory of photoluminescence excitation spectroscopy in semiconductors
Authors: Hannewald Karsten , Glutsch Stephan , Bechstedt Friedhelm 
Published: July 2003

AbstractWe present a microscopic theory of photoluminescence excitation spectroscopy (PLE) in semiconductors that is not restricted to thermalized carrier distributions. The phenomenological assumption of equivalence between PLE and absorption spectra is confirmed only for thermal equilibrium. For nonequilibrium, i.e, small time intervals between laser‐pulse excitation and luminescence detection, our quantum‐kinetic simulations reveal significant differences between PLE and absorption signals which can be attributed to incomplete relaxation and bottleneck effects, and should be observable in experiment.
Anomalously fast decay of the LH–HH exciton Raman coherence
Authors: Borca C. N. , VanEngen Spivey Amelia G. , Cundiff Steven T. 
Published: July 2003

AbstractWe perform 3‐pulse transient four‐wave‐mixing on a GaAs/AlGaAs multiple quantum well. This allows us to measure both the decay of the Raman coherence between the heavy‐hole and light‐hole excitons and the decay of the respective optical coherences. We observe that the decay rate of the Raman coherence is greater than the sum of decay rates of the optical coherences. This cannot happen within a Markov approximation for the scattering processes, as verified by simulations. The simulations show that such behavior can occur only in the presence of anti‐correlated scattering processes in a non‐Markovian regime.
Microscopic theory for the nonlinear optical response of the Si(111)‐(2×1) surface exciton
Authors: Reichelt M. , Meier T. , Rohlfing M. , Koch S. W. 
Published: July 2003

AbstractA novel microscopic approach for computing nonlinear optical properties of semiconductor surfaces is outlined. The linear and nonlinear response of the Si(111)‐(2×1) surface is studied using a combination of ab‐initio band‐structure theory and equation of motion technique. The usefulness of the method is shown by reproducing known excitonic effects in the linear differential reflectivity spectrum. To additionally demonstrate the applicability of the approach for the nonlinear regime, the nonlinear optical response in Stark effect configuration is examined.
Non‐classical excitonic transport in quantum wells
Authors: Zhao Hui , Dal Don B. , Moehl S. , Kalt H. 
Published: July 2003

AbstractWe report investigations on excitonic transport in ZnSe quantum wells using far‐field nano‐photoluminescence enhanced by a solid immersion lens. The 250‐nm spatial resolution and 5‐ps temporal resolution allow the access to non‐classical transport regimes. From zero‐phonon‐line spectroscopy we deduce the spatial distribution of the PL intensity under different cw excitation condition and its temporal evolution after a pulsed excitation, respectively. The periodic quenching of the transport length as function of excitation excess energy and the nonlinear expansion of the PL spot observed in time‐resolved experiments reveal the dominance of hot‐exciton effects. The experimental data are well modelled by a Monte Carlo simulation. Spatially resolved phonon‐sideband spectroscopy is used to observe directly the coherent transport and the energy relaxation of hot excitons during transport. The coherence length is measured to be 300–400 nm at low temperatures and the excitons are found to remain hot during transport on a length scale of several micrometers.
Spin‐sensitive bleaching and spin relaxation in QWs
Authors: Schneider Petra , Ganichev S. D. , Kainz J. , Rössler U. , Wegscheider W. , Weiss D. , Prettl W. , Bel'kov V. V. , Golub L. E. , Schuh D. 
Published: July 2003

AbstractSpin‐sensitive saturation of absorption of infrared radiation has been investigated in p‐type GaAs QWs. It is shown that the absorption saturation of circularly polarized radiation is mostly controlled by the spin relaxation time of the holes. The saturation behavior has been investigated for different QW widths and in dependence on the temperature with the result that the saturation intensity substantially decreases with narrowing of QWs. Spin relaxation times were experimentally obtained by making use of calculated (linear) absorption coefficients for inter‐subband transitions.
Signatures of biexcitons and triexcitons in coherent non‐degenerate semiconductor optics
Authors: Meier T. , Sieh C. , Finger E. , Stolz W. , Rühle W. W. , Thomas P. , Koch S. W. , Wieck A. D. 
Published: July 2003

AbstractSignatures of exciton and two‐exciton states in semiconductor systems are investigated experimentally and theoretically. A set of quantum well samples with different well widths is studied using coherent excitation spectroscopy. The experimental results are analyzed using a microscopic model demonstrating the importance of biexciton correlations and disorder effects. Additional numerical investigations of absorption changes in small nanorings are employed to analyze optical transitions from two‐exciton to three‐exciton resonances.
Exciton fine structure in interfacial quantum dots
Authors: Phillips R. T. , Steffan A. G. , Newton S. R. , Reinecke T. L. , Kotlyar R. 
Published: July 2003

AbstractWe have studied, by ‘micro‐magneto‐photoluminescence’, the eigenstates of excitons localised in the interfacial potential of narrow GaAs/Al0.31Ga0.69As quantum wells. These behave in many respects as quantum dot excitons, and give narrow emission lines that permit direct resolution of Zeeman splittings. Some dots show small zero‐field splitting (<100 μeV), varying down to below the limit of resolution of our technique (≈25 μeV). For these dots the excitonic g‐factor depends on well‐width, and also shows variation with the applied field B. The variation with B is related to the band mixing which is more prominent in these weakly‐confined dots than in, for example, typical Stranski–Krastanow dots. The magnitude of the term linear in B can be calculated in a simplified model of the confined state, which gives a method of estimating the lateral extent of the confining potential. For particular transitions which are found at the extreme low‐energy end of the emission from wells of 2 nm and 3 nm width, a different behaviour is found. These show much larger zero‐field splitting of around 1 meV, and much smaller diamagnetic shift than that in the more usual dots with small zero‐field splitting. The measured spin fine structure of these states is compared with that calculated from a spin Hamiltonian for a heavy‐hole exciton, which gives a unique determination of the full three‐dimensional g‐factor for a single quantum dot.
Generation of strongly polarization‐correlated photon pairs by cascaded emission from individual CdSe/ZnSe quantum dots
Authors: Ulrich S. M. , Strauf S. , Michler P. , Bacher G. , Forchel A. 
Published: July 2003

AbstractBy combined pulsed auto‐ and cross‐correlation measurements (4 K) on individual self‐assembled CdSe quantum dots, besides triggered single photon emission promising for high repetition frequencies, in particular the generation of time‐correlated photon pairs from the sequential radiative biexciton‐exciton decay is demonstrated. For the photon pairs a strong collinear polarization degree up to 84.5% was observed which is related to an exciton fine‐structure splitting. Together with the measured exciton lifetime an estimate for the relaxation time (≥480 ps) between the fine‐structure levels is given.
K‐dependent exchange interaction of quadrupole excitons in Cu2O
Authors: Dasbach G. , Fröhlich D. , Stolz H. , Klieber R. , Suter D. , Bayer M. 
Published: July 2003

AbstractThe long‐ and short‐range exchange interaction for the quadrupole allowed transition to the yellow 1S orthoexciton in Cu2O is derived. While the three orthoexciton states still remain degenerate, when treating the exchange up to the order of K‐linear terms, a fine structure arises when K‐quadratic terms are included. This splitting is investigated experimentally by high resolution spectroscopy. Exchange contributions of few μeV are resolved and compared to theory. The impact of strain on the exciton fine structure is discussed and evaluated.
Direct observation of all‐optical injection of spin‐polarized currents
Authors: Hübner J. , Klude M. , Hommel D. , Bhat R. D. R. , Sipe J. E. , van Driel H. M. , Rühle W. W. 
Published: July 2003

AbstractBallistic currents of spin‐polarized carriers are generated by quantum interference of one and two photon absorption. Polarization and relative phase of the exciting femtosecond laser fields control the magnitude and direction of the currents as well as the electron spin orientation. These spin‐polarized currents are experimentally detected by a phase‐dependent spatial shift of the circularly analyzed photoluminescence in cubic ZnSe.
Exciton–phonon interaction in semiconductors with intermediate polar coupling
Authors: Schäfer W. , Gartner P. , Jahnke F. 
Published: July 2003

AbstractThe importance of vertex corrections in the description of the absorption spectra in semiconductors is discussed. These corrections are responsible for the excitonic correlation of the phonon‐scattered carriers and it is shown that these correlations are essential for the description of excitonic sidebands in the case of intermediate coupling. Different approximation schemes are compared in numerical examples.
Dynamics of two‐pair correlations induced by simultaneous excitation of excitonic and band‐to‐band continuum transitions
Authors: Wühr J. , Axt V. M. , Kuhn T. 
Published: July 2003

AbstractThe impact of all kinds of two‐pair correlations (biexcitons, exciton–exciton scattering states, two free electron–hole pairs) on four‐wave‐mixing (FWM) signals generated by ultra‐short optical pulses that simultaneously excite excitons and free electron–hole pairs is analyzed. Signatures of two‐pair correlations are identified by comparing the full theory with mean‐field (MF) results. For systems with strong exciton binding two‐pair correlations suppress changes of the line width of the excitonic emission that are predicted by the MF theory when the central excitation energy is varied above the band edge. For systems with weakly bound excitons the presence of two‐pair correlations leads to an emission in between the exciton and the band edge with a complex line shape which strongly depends on the excitation energy.
Camouflage third‐harmonic generation in the nonperturbative few‐cycle regime
Authors: Tritschler T. , Mücke O. D. , Morgner U. , Kärtner F. X. , Wegener M. 
Published: July 2003

AbstractFocusing 5 fs optical pulses, with a Rabi energy comparable to the carrier photon energy, derived from a mode‐locked Ti:sapphire laser oscillator onto ZnO crystals, leads to large contributions in the emitted light, which depend on the carrier‐envelope offset frequency of the laser oscillator. Moreover, we discuss that an additional contribution at twice the carrier‐envelope offset frequency is due to camouflage third‐harmonic generation – a process, which looks like second‐harmonic generation in an inversion symmetric medium at first sight.
Electronic properties of superconducting NbSe2 nanotubes
Authors: Ivanovskaya V. V. , Enyashin A. N. , Medvedeva N. I. , Ivanovskii A. L. 
Published: July 2003

AbstractAtomic models of zigzag (n,0)‐ and armchair (n,n)‐like nanotubes (n = 7–58) of the superconducting NbSe2 are constructed and their electronic properties and bond indices are investigated using the tight‐binding band theory. The calculations performed show that all the considered NTs are uniformly metallic‐like. The density of states at the Fermi level contains a considerable contribution from Nb4d states, which will be significant for the superconductivity. The stability and electronic properties of the NbSe2 NTs depend on the atomic configuration and diameter of the tubes. Nb—Se covalent bonds were found as basic in NbSe2 tubes. According to our estimations, zigzag‐like configurations of the NbSe2 nanotubes are more stable.
Papers presented at the 7th International Workshop on Nonlinear Optics and Excitation Kinetics in Semiconductors (NOEKS 7)
Authors: Wegener Martin 
Published: July 2003

AbstractThe 7th International Workshop on Nonlinear Optics and Excitation Kinetics in Semiconductors (NOEKS 7) was held at Uni‐versit�t Karlsruhe from 24‐28 February 2003. Topics of NOEKS 7 were: Ultrafast dynamics (coherent effects, coherent control, quantum kinetics, THz‐experiments), photonic crystals (2D and 3D photonic band gap materials), quantum dot physics (quantum dots, quantum wires), spin effects (spin dephasing, spin transport), disorder‐related effects, organic semiconductors, semiconductor quantum optics (luminescence, photon statistics), device physics (quantum cascade lasers, superlattices, interband lasers), and Bose‐Einstein condensation of excitons.The cover picture is taken from Ref. [1] and shows the spatial pattern of the indirect exciton PL intensity in GaAs/AlGaAs coupled quantum wells. Around the laser excitation spot, it ex‐hibits an external ring structure with a periodic array of circular‐shaped structures which is due to the formation of an exciton gas with macroscopic coherence.The full proceedings of NOEKS 7, guest‐edited by Martin Wegener, are published in physica status solidi (c) 0, No. 5 (2003). Since 1988, all previous NOEKS proceedings have also appeared in physica status solidi.
Kinetic isotope effects in the active site of B. subtilis chorismate mutase
Authors: Worthington Sharon E. , Roitberg Adrian E. , Krauss Morris 
Published: July 2003

AbstractKinetic isotope effects are determined for the enzyme‐catalyzed Claisen rearrangement of chorismate to prephenate using computational methods. The calculated kinetic isotope effects (KIEs) compare reasonably with the few available experimental values with both the theory and experiment obtaining a large KIE for the ether oxygen, indicating large polarization of the transition‐state geometry. Because there is a question of the extent that the experimental rate constants are for chemistry as the rate‐limiting step, the KIEs for all the atoms of the substrate are reported with the exception of the carboxylate groups. A substantial number of large regular and inverse isotope effects are predicted for the hydrogens on the cyclohexadienyl ring related to activation of the reactant and charge reorganization in the transition state. A large KIE is predicted for the hydrogen atom bound to the ether carbon atom because the largest valency change and charge transfer occurs at the ether bond in both the reactant and tansition state. Observation of the overall pattern of predicted KIEs would ensure that conditions are favorable for the rate‐limiting chemistry. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 287–292, 2003
DFT study on cooperativity in the interactions of hydrazoic acid clusters
Authors: Xia Qi Ying , Xiao He Ming , Ju Xue Hai , Gong Xue Dong 
Published: July 2003

AbstractDensity functional theory at the B3LYP level with the 6‐311G** basis set is performed to calculate the systems consisting of up to four hydrazoic acid molecules. The dimers are found to exhibit cyclic and chain structures with N … H contacts at ca. 2.1–2.7 Å. However, there are only cyclic structures with N … H contacts at ca. 2.0–2.3 Å and 2.0–2.1 Å in the trimer and tetramer, respectively. Hydrogen bond distances in the trimer and tetramer are shorter than those in the cyclic dimer as a result of the stronger interaction between molecules. The contribution of cooperative effect to the interaction energy is significant. After the correction of the basis set superposition error and zero‐point energy, the binding energies are −10.69, −29.34, and −54.26 kJ·mol−1 for the most stable dimer, trimer, and tetramer, respectively. The calculated IR shifts for NH stretching mode increase with the size of the cluster growths, reaching more than 200 cm−1 in the tetramer. For the most stable clusters, the transition from the monomer to dimer, dimer to trimer, and trimer to tetramer involve changes of −14.40, −25.68, and −31.88 kJ·mol−1 for the enthalpies at 298.15 K and 1atm, respectively. We also perform Mulliken populations analysis and find the Mulliken populations on intermolecular N … H increasing in the sequence of the dimer, trimer, and tetramer. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 279–286, 2003