Parametric relaxation in whispering gallery mode exciton-polariton condensates

Abstract

Polariton condensation of one-dimensional multimode whispering gallery mode exciton polaritons is investigated in hexagonal ZnO microwires at cryogenic temperatures. At threshold, stimulated scattering is fed by the resonant emission from highly populated defect-bound excitons. With further increasing excitation power, condensates relax within the multimode whispering gallery mode polariton ladder, leading to their effective evaporative cooling. The relaxation is a parametric polariton-polariton scattering process evidenced by its intensity, energy, and momentum evolution. The experimental observations are in good agreement with numerical simulations based on a model for polariton-polariton scattering extended to the multimodal whispering gallery mode system.