S. Bar-Ad

Magnetically Enhanced Exciton-exciton Correlations In Semiconductors

We present investigations of fs time resolved coherent wave mixing under high magnetic field. Our experiments reveal a new regime at high magnetic field and low excitation density dominated by the Coulomb interaction. This regime is inconsistent with the semiconductor Bloch equations. A model which includes exciton-exciton correlation successfully describes many features of this regime. {copyright} {ital 1997} {ital The American Physical Society}

Quantum Confined Fano Interference

Quantum size effects have been thoroughly investigated since advances in material synthesis made possible the growth of semiconductor heterostructures with atomic monolayer accuracy. They become apparent in a physical phenomenon when at least one dimension of the sample becomes comparable to or smaller than the length scale that governs the quantum mechanics of that phenomenon. In the optical domain the exciton Bohr radius ao is usually the relevant length scale, and quantum confinement dominates the optical properties of semiconductor structures of size L # ao [1,2]. In the case of transport the carrier de Broglie wavelength lB determines the length scale at which quantum transport effects are observed [3]. In this Letter we present a new example of quantum size effects, apparent in the line shape of an optical resonance

Ultrafast coherent spectroscopy of one-dimensional magnetoexcitons in semiconductors

Abstract We investigate the ultrashort coherent dynamics of one-dimensional Fano andvLorentzian magnetoexcitons in GaAs using temporally and spectrally resolved four-wave mixing (FWM). The dephasing time of a Fano resonance is intrinsically limited by the coupling between discrete states and continua which is responsible for Fano interference. In contrast, the coherent emission from Lorentzian magnetoexcitons dephases solely due to quasi-particle scattering, dominated by exciton-exciton scattering at low temperatures. We find a very fast decay of the time-integrated FWM signal from Fano magnetoexciton resonances. This decay is not due to dephasing. The quenching of the FWM signal for non-overlapping excitation pulses is the result of quantum interference. This destructive quantum interference is not observed for purely Lorentzian dynamics. For the simultaneous excitation of Lorentzian and Fano magnetoexciton resonances, destructive quantum interference also quenches the coherent emission from Lorentzian magnetoexcitons due to quantum mechanical coupling between the different resonances.

Coherent dynamics and dephasing of one-dimensional magnetoexcitons in GaAs

We study the ultrashort dynamics and the dephasing processes of one-dimensional Lorentzian and Fano magnetoexcitons in GaAs, using temporally and spectrally resolved four-wave mixing. The dephasing of the Lorentzian magnetoexcitons is determined by quasi-particle scattering, dominated by exciton – exciton scattering at low temperatures. In contrast, the dephasing time of the Fano magnetoexcitons is intrinsically limited by the Fano coupling to the continuum. Quantum interference is observed if Fano magnetoexcitons contribute to the four-wave mixing signal. This effect is absent in the case of purely Lorentzian dynamics. We show that Lorentzian and Fano magnetoexciton resonances are coupled by Coulomb correlation and discuss the consequences of this coupling.

Photocarrier relaxation in the quantum kinetics regime

Summary form only given. We present a study of carrier relaxation in bulk GaAs at room temperature in the quantum kinetics regime. We use a modified frequency-resolved pump-probe technique with pump and probe durations independently adjustable from 30-100 fs. Differential absorption spectra (DAS) for 70-fs pump and probe at low excess energy is presented.