M. Hübner

Theory of coherent effects in semiconductors

A microscopic theory is applied to discuss coherent excitation effects in semiconductors. The theory is evaluated to analyze ultrafast absorption changes around the exciton resonance in semiconductor quantum-well structures where the relative strength of the different many-body contributions can be manipulated by proper selection of pump and probe polarizations. For two-band systems and oppositely circular polarization it is shown that Coulombic correlation dynamics dominates the optical response. As a consequence, the optical Stark effect in this configuration corresponds to a red shift of the exciton resonance in striking contrast to the usual atomic-like blue shift. The predictions are confirmed by experiments using high-quality InGaAs quantum-well systems.

Quantum correlations in semiconductor microcavities

The quantum mechanical nature of the light field in semiconductor microcavities leads to non-classical coupling effects between photons and electron–hole excitations. It is shown that these quantum correlations give rise to characteristic corrections of the semiclassical light-matter coupling dynamics. Examples of quantum correlation signatures include entanglement effects in the probe reflection of a microcavity system and squeezing in the incoherent emission.

Quantum correlations in a semiconductor microcavity

Summary form only given. The nonlinear optical response of semiconductor microcavities in the nonperturbative regime has been the subject of many recent experiments. Contrary to clear demonstrations of the quantized nature of the vacuum-field Rabi splitting of a single atom, most of the experiments on semi-conductor microcavities could be explained in terms of a classical light field. Only recently, quantized light field effects have been reported in a coherent control experiment (Lee et al, 1999) and theoretically investigated in secondary emission (Kira et al, 1999). Here, results are presented that display a pronounced third transmission maximum lying energetically between the two normal modes. The third peak can be observed in resonant femtosecond single-beam as well as picosecond pump-probe experiments under various excitation conditions.

Signatures of polaritonic normal modes in the photoluminescence from periodic multiple quantum well structures following continuum excitation

Summary form only given. Several studies have demonstrated the strong influence of radiative exciton coupling on the resonant optical response of periodic quantum well (PQW) structures in the vicinity of the heavy-hole (hh)-exciton Bragg resonance for d=/spl lambda//2, where d is the distance between adjacent quantum wells (QWs) and /spl lambda/ is the hh-exciton resonance wavelength inside the structure. In this work, we present photoluminescence (PL) experiments on high quality InGaAs/GaAs PQW structures with up to N=100 QWs, where the exciton emission is strongly influenced by the coherent interwell coupling, showing up in multiple line-splitting and a crossing of the normal modes around Bragg resonance. For N/spl ges/30 and certain ds we find a quadratic increase of the amplitude and an increasing directionality of the vertical (perpendicular to QWs) emission. The weakest emission occurs in Bragg resonance, where under resonant excitation a strong superradiant reemission takes place.

Influence of carrier-correlations on the optical Stark effect of semiconductors

Summary form only given. For a proper understanding of nonlinear optical experiments in semiconductors even the low-density limit Coulomb-induced many body correlations beyond the Hartree-Fock decoupling scheme need to be considered. In the coherent X(3) limit these correlations manifest themselves in the contributions of bound and unbound two-exciton states to the optical response. The understanding of nonlinear excitonic effects in the Stark effect of semiconductors including carrier-correlations is still of fundamental interest.