High-energy side-peak emission of exciton-polariton condensates in high density regime

TL;DR

This paper reports the discovery of a high-density photoluminescence sideband in exciton-polariton condensates, revealing persistent strong coupling beyond the Mott density, which challenges conventional understanding of semiconductor lasers.

Contribution

It presents the first observation of a high-density sideband in exciton-polariton systems, indicating sustained strong coupling at densities near the Mott transition.

Findings

Observation of a novel photoluminescence sideband at high densities

The sideband's energy separation depends on excitation power

Persistent coherent electron-hole-photon coupling at high densities

Abstract

In a standard semiconductor laser, electrons and holes recombine via stimulated emission to emit coherent light, in a process that is far from thermal equilibrium. Exciton-polariton condensates -- sharing the same basic device structure as a semiconductor laser, consisting of quantum wells coupled to a microcavity -- have been investigated primarily at densities far below the Mott density for signatures of Bose-Einstein condensation. At high densities approaching the Mott density, exciton-polariton condensates are generally thought to revert to a standard semiconductor laser, with the loss of strong coupling. Here, we report the observation of a photoluminescence sideband at high densities that cannot be accounted for by conventional semiconductor lasing. This also differs from an upper-polariton peak by the observation of the excitation power dependence in the peak-energy separation. Our interpretation as a persistent coherent electron-hole-photon coupling captures several features of this sideband whereas many remain elusive. Understanding the observation will lead to a development in non-equilibrium many-body physics.