2012 Volume 67 Issue 2 Pages 96-107
An exciton-polariton is a hybrid quasi-particle (elementary excitation) consisting of strongly coupled quantum well exciton and planar microcavity photon. Since the effective mass of an exciton-polariton is four orders of magnitude lighter than the exciton mass and ten orders of magnitude lighter than the alkali atom mass, the exciton-polariton is expected to satisfy a quantum degeneracy condition and feature dynamic condensation at high temperatures and low densities. In contrast to superfluid He liquids and dilute atomic Bose-Einstein condensates at thermal equilibrium condition, the exciton-polariton condensate is inherently a non-equilibrium open system so that it may open new frontiers in statistical mechanics. In this review article, we will focus on the distinction between the exciton-polariton condensation and normal laser oscillation, the experimental evidences for the Berezinskii-Kosterlitz-Thouless phase transition, the Bogoliubov excitation spectrum and the dynamical condensation at high orbital p-wave or d-wave states.