Theoretical Study of Exciton-Polariton Condensates in Semiconductor Microcavities

Abstract

Exciton-polaritons are half-light and half-matter quasi-bosons arising in a two-dimensional semiconductor microcavity from the strong-coupling between an exciton and a photon Exciton-polariton condensate in the microcavities are formed through the stimulated accumulation of low-energy polaritons above a threshold pumping because of the intrinsic light mass from the phtonic component and the interaction from the excitonic component The features indicating the condensation include the temporal or spatial coherence that extends over th entire condensate the appearance of quantized vortices the modified excitation spectrum as well as the robustness of the condensate profile againist the disorders (superfluidity) and so on Therefore it is essential to study the dynamics of polariton condensates in order to search for the rich or promising physical effects that could provide further experimental demonstration This thesis uses the complex Gross-Pitaevskii equation to study the condensate states of the exciton-polaritons with a finite-size pumping spot Two methods are used to deal with the dynamics of the condensates One is using a single partial differential equation incorporating the pumping gain and dissipative terms directly into the conventional Gross-Pitaevskii equation; and the other considers the relaxation mechanism from the reservoir and the polariton is consistently replenished from the reservoir After the polariton condensate states under a harmonic confinement have been numerically calculated we studied the dynamic instabilities for a given pumping scheme by using the Bogoliubov perturbation theory A phase diagram was therefore obtained with respect to the pump power and pump spot Under this framework the superfluid properties such as drag force and critical velocities quantized vortices BKT transition and super-currents can be separately discussed Next the system is expanded in an one-dimensional periodic potential We obtain the nonlinear band structures from which we understand how the transition between 0-state and ?-state occurs We also gave the evidences of the synchronization conditions of a two-component spinor condensate with self-interaction and inter-component hopping Finally we studied the half-quantum vortices in a pumping scheme with tunable degree of polarization The inhomogeneous polarization texture and the effects of a Gaussian pinning were studied

Date of Award	2014 Jul 9
Original language	English
Supervisor	Ming-Dar Wei (Supervisor)