Ground-state and spectral signatures of cavity exciton-polariton condensates

Abstract

We propose a projector-based renormalization framework to study exciton-polariton Bose-Einstein condensation in a microcavity matter-light system. Treating Coulomb interaction and electronhole/photon coupling effects on an equal footing, we analyze the ground-state properties of the exciton-polariton model according to the detuning and the excitation density. We demonstrate that the condensate by its nature shows a crossover from an excitonic insulator (of Bose-Einstein, respectively, BCS type) to a polariton and finally photonic condensed state as the excitation density increases at large detuning. If the detuning is weak, polariton or photonic phases dominate. While in both cases a notable renormalization of the quasiparticle band structure occurs that strongly affects the coherent part of the excitonic luminescence, the incoherent wave-vector-resolved luminescence spectrum develops a flat bottom only for small detuning.

Thermal fluctuations in a system of microcavity exciton‐polariton condensations

“…Without loss of generality, we choose the cavity frequency . The physical scenario is not much different unless the cavity frequency is larger than the width of the bare band structure (). In the calculation below, we limit itself at a positive detuning.…”

“…Cavity polariton condensed at room temperature has been observed in experiments . On the theoretical side, the BEC exciton‐polariton condensation scenario in a microcavity has been studied intensively, however, mainly for the ground state, i.e., at zero temperature . In a microcavity, polaritons generally cannot condense as a BEC at finite temperature because they are two‐dimensional (2D) particles, but they are subjected to the Kosterlitz–Thouless (KT) phase transition toward a superfluid phase ().…”

“…In this paper, we study thermal fluctuations affecting the exciton‐polariton system in a microcavity. Although experiments are usually performed away from equilibrium, there are reasons also to study the stationary state of a closed microcavity polariton system . On the one hand, the quality of microcavity fabrication and of mirrors will improve, so that the experimental situation will become closer to thermal equilibrium.…”

“…In the past, as a version of mean‐field theories, a variational treatment has been used to study the cavity polariton problems but only at zero temperature (). That mean‐field approximation can be corrected, for instance, by a projector‐based renormalization method allowing to incorporate fluctuation processes . However, due to the calculation being cumbersome, application of the method to the polariton problem is limited to the one‐dimensional situation only (), that is not the case of the problem in a microcavity in which the polaritons are 2D quasiparticle ().…”

Theory of zero‐phonon decay luminescence of semiconductor excitons

“…The most obvious evidence, of course, would be the detection of coherence. On the other hand, an exciton condensate is also reflected in the luminescence and photon spectra . Theory must provide, therefore, an approach both to coherence as well as spectral properties of the luminescence signal.…”