D. N. Krizhanovskii

Nonlinear dynamics of polariton scattering in semiconductor microcavity: Bistability vs. stimulated scattering

We investigate an unusual behavior of the parametric polariton scattering in a semiconductor microcavity (MC) under a strong cw resonant excitation: The maximum of the scattered signal above the threshold of stimulated parametric scattering does not shift along the microcavity lower polariton branch with the change of pump detuning or angle of incidence, but is fixed at normal direction. We show that such a behavior can be modelled numerically by a system of Maxwell and nonlinear Schrodinger equations for cavity polaritons and explained via the competition between the bistability of a driven nonlinear MC polariton and the instabilities of parametric polariton-polariton scattering.

Polarization Bistability and Resultant Spin Rings in Semiconductor Microcavities

The transmission of a pump laser resonant with the lower polariton branch of a semiconductor microcavity is shown to be highly dependent on the degree of circular polarization of the pump. Spin dependent anisotropy of polariton-polariton interactions allows the internal polarization to be controlled by varying the pump power. The formation of spatial patterns, spin rings with a high degree of circular polarization, arising as a result of polarization bistability, is observed. A phenomenological model based on effective semiclassical equations of motion provides a good description of the experimental results. Inclusion of interactions with the incoherent exciton reservoir, which provides spin-independent blueshifts of the polariton modes, is found to be essential.

Stimulated Polariton Scattering in Semiconductor Microcavities: New Physics and Potential Applications

Stimulated polariton scattering in semiconductor microcavities is reported. The phenomena arise from the bosonic character of the coupled exciton-photon modes of the system. The ability to manipulate and control the polariton dispersions in microcavities is shown to be a key factor underlying the new observations. The potential of such phenomena to form the basis of a new type of coherent light source (polariton lasers) and highly efficient optical parametric oscillators is discussed.

Nonlinear effects in a dense two-dimensional exciton-polariton system in semiconductor microcavities

Angle resolved emission spectra of microcavities with quantum wells embedded in the active layer have been investigated under the resonant and quasi-resonant excitation into the lower polariton (LP) branch. The conditions have been found at which macroscopic filling of polariton modes is reached in the strong coupling regime. The strong nonlinear effects in the intensity and the degree of polarization of polariton emission have been observed and investigated. Both experimentally observed renormalization of the dispersion and strong narrowing of polariton mode have been explained using an interacting polariton model predicting that the coupling between the LP mode ELP(k) and the mode of composite polaritons ECP(k) = 2ω(k0)-ELP(2kexcitation-k) is qualitatively different from that of the exciton and photon.

Energy relaxation of resonantly excited polaritons in semiconductor microcavities

Abstract Polariton emission has been investigated in a GaAs based microcavity under various excitation conditions which excite predominately hot free excitons and carriers (He–Ne laser excitation), localized excitons (Ti–sapphire laser excitation), or mixed system. Strong differences have been found both in the intensity, the energy distribution, and the temperature dependence of polariton emission for the different excitation conditions. The relaxation into the low polariton branch due to consecutive scattering via polariton states in the bottleneck region and via the states of localized excitons has been found ineffective. Instead, we found that the highly effective filling of low polariton states occurs via relaxation of mobile excitons delocalized due to either thermal activation or interaction with hot carriers.

Impact of exciton localization on the optical non-linearities of cavity polaritons

Abstract Polaritons in a semiconductor microcavity excited below the free exciton energy have been studied by pump-and-probe experiments. The excitation results in a blue shift of the transmission peak of the lower polariton branch, followed by a strong enhancement and narrowing. These changes are opposite to those caused by high above band gap excitation. The strong differences between resonant and non-resonant excitation result from a different impact of localized excitons and unbound carriers on the quantum well susceptibility. The experimental observations are modeled in the approximation of nonperturbative coupling of the exciton system to the cavity light field.

Temperature Dependence and Non‐Linear Polarization Properties of Parametric Polariton Scattering in Semiconductor Microcavities

Polariton-polariton scattering is studied in a III-V microcavity (MC) by cw polarized photoluminescence techniques using resonant excitation into the lower polariton (LP) branch. Such excitation conditions allow the parametric process leading to the creation of macroscopic coherent populations of the signal and idler final states. The stimulated scattering into these modes is found to be resonantly enhanced under elliptically polarized excitation when a transition to the singlet biexciton intermediate state is allowed. The influence of dephasing mechanisms on coherence effects in strongly optically driven MCs, and the origin of energy renormalization of the signal and idler modes is investigated from a study of the temperature dependence of the parametric scattering.

Impact of exciton localization on cavity polaritons

Abstract Polariton emission was investigated in a GaAs-based microcavity (MC) under various excitation conditions which excite predominately hot excitons and carriers, localized excitons, or a mixed system. Strong differences have been found both in the intensity, the energy distribution, and the temperature dependence of the lower branch polariton (LP) emission for the different excitation conditions. In MCs with negative detuning, LP states are filled via relaxation of mobile excitons delocalized due to either thermal activation or interaction with hot carriers. In MCs with positive detuning, in contrast, the energy relaxation of photoexcited LPs is more effective whereas an additional above-band-gap excitation leads to a strong decrease of population at the LP band bottom.

Effect of the modulation of the polariton potential on the polarization instability of stimulated polariton-polariton scattering in planar gaas microcavities

The polarization characteristics of the stimulated polariton-polariton scattering signal under resonance excitation in the vicinity of the inflection point of the polariton dispersion curve are investigated in the absence and in the presence of exciton-potential modulation imposed by a surface acoustic wave. It is found that the spatial modulation of the exciton potential leads to an abrupt decrease in the effective critical pump density above which the polarization of the scattering signal changes. This opens the way for the use of acoustic waves to control the polarization of the stimulated scattering signal in polariton systems.

Energy relaxation of excitonlike polaritons in semiconductor microcavities: Effect on the parametric scattering of polaritons

Polariton emission in GaAs-based microcavities has been studied under variable conditions, which made it possible to excite (a) polaritons from the upper polariton branch and hot free polaritons and electrons, (b) polaritons from the lower polariton branch (LPB) and localized excitons, and (c) the mixed system. Variation of the excitation conditions leads to substantial differences in the energy distributions of polaritons and in the temperature dependences of polariton emission. It is established that the energy relaxation of resonantly excited LPB polaritons via polariton and localized exciton states at liquid helium temperatures is ineffective. Instead, the relaxation bottleneck effect is suppressed with increasing temperature by means of exciton delocalization (due to thermal excitation by phonons). The most effective mechanism of relaxation to the LPB bottom is via scattering of delocalized excitons on hot free carriers. It is found that the slow energy relaxation of polaritons excited below the free exciton energy can be significantly accelerated at low temperatures by means of additional weak generation of hot excitons and, especially, hot electrons. This acceleration of the energy relaxation of polaritons by means of additional overbarrier photoexcitation sharply decreases the barrier for stimulated parametric scattering of polaritons excited at an LPB inflection point. Therefore, additional illumination can be used to control the polariton-polariton scattering.