Study of ortho-to-paraexciton conversion in Cu$_2$O by excitonic Lyman spectroscopy

TL;DR

This study uses time-resolved excitonic Lyman spectroscopy to investigate the ultrafast conversion of orthoexcitons to paraexcitons in Cu$_2$O, revealing a density-dependent spin exchange process relevant for Bose-Einstein condensation.

Contribution

It provides new insights into the dynamics of exciton conversion in Cu$_2$O using femtosecond spectroscopy, highlighting the role of spin exchange in the process.

Findings

Fast, density-dependent ortho-to-paraexciton conversion observed

Spin exchange between exciton pairs drives the conversion

Implications for paraexciton Bose-Einstein condensation discussed

Abstract

Using time-resolved $1s$-$2p$ excitonic Lyman spectroscopy, we study the orthoexciton-to-paraexcitons transfer, following the creation of a high density population of ultracold $1s$ orthoexcitons by resonant two-photon excitation with femtosecond pulses. An observed fast exciton-density dependent conversion rate is attributed to spin exchange between pairs of orthoexcitons. Implication of these results on the feasibility of BEC of paraexcitons in Cu$_2$O is discussed.