Bose-Einstein condensation in semiconductors: the key role of dark excitons

TL;DR

This paper explores how the non-elementary bosonic nature of excitons influences Bose-Einstein condensation in semiconductors, highlighting the key role of dark excitons and their interactions with bright states.

Contribution

It reveals the impact of dark excitons on Bose-Einstein condensation and demonstrates their influence on polarization and observable shifts in exciton lines.

Findings

Dark excitons dominate the condensate in bulk semiconductors.

Bright and dark states are coupled through Pauli exclusion and Coulomb interactions.

Dark condensates induce measurable shifts in bright exciton lines.

Abstract

The non elementary-boson nature of excitons controls Bose-Einstein condensation in semiconductors. Composite excitons interact predominantly through Pauli exclusion; this produces dramatic couplings between bright and dark states. In microcavities, where bright excitons and photons form polaritons, they force the condensate to be linearly polarized--as observed. In bulk, they also force linear polarization, but of dark states, due to interband Coulomb scatterings. To evidence this dark condensate, we thus need indirect processes, like the shift it induces on the (bright) exciton line.