Spectroscopic Signatures for the Dark Bose-Einstein Condensation of Spatially Indirect Excitons

TL;DR

This study provides spectroscopic evidence for the dark Bose-Einstein condensation of spatially indirect excitons in a GaAs bilayer, highlighting the transition to a predominantly dark, macroscopically occupied excitonic state at ultra-low temperatures.

Contribution

It demonstrates the spectroscopic signature of dark exciton condensation in a semiconductor system, a phenomenon previously unobserved in such dilute regimes.

Findings

Optically bright excitonic states are depleted at sub-Kelvin temperatures.

Dark excitonic states become macroscopically occupied during condensation.

Condensation occurs below a critical temperature of about 1K in a dilute regime.

Abstract

We study semiconductor excitons confined in an electrostatic trap of a GaAs bilayer heterostructure. We evidence that optically bright excitonic states are strongly depleted while cooling to sub-Kelvin temperatures. In return, the other accessible and optically dark states become macroscopically occupied so that the overall exciton population in the trap is conserved. These combined behaviours constitute the spectroscopic signature for the mostly dark Bose-Einstein condensation of excitons, which in our experiments is restricted to a dilute regime within a narrow range of densities, below a critical temperature of about 1K.