Electron-hole pair condensation at the semimetal-semiconductor transition: a BCS-BEC crossover scenario

TL;DR

This paper explores how tuning Coulomb attraction in a solid-state system can induce a continuous crossover from BCS-like electron-hole pairing to Bose-Einstein condensation of excitons, explaining transport anomalies in correlated materials.

Contribution

It demonstrates, through the extended Falicov-Kimball model, that a BCS-BEC crossover can occur at the semimetal-semiconductor transition in solids, a novel insight into excitonic insulators.

Findings

Crossover between BCS-like and BEC-like electron-hole pairing.

Transport anomalies linked to precursor effects of the crossover.

Potential realization in strongly correlated mixed-valence compounds.

Abstract

We act on the suggestion that an excitonic insulator state might separate---at very low temperatures---a semimetal from a semiconductor and ask for the nature of these transitions. Based on the analysis of electron-hole pairing in the extended Falicov-Kimball model, we show that tuning the Coulomb attraction between both species, a continuous crossover between a BCS-like transition of Cooper-type pairs and a Bose-Einstein condensation of preformed tightly-bound excitons might be achieved in a solid-state system. The precursor of this crossover in the normal state might cause the transport anomalies observed in several strongly correlated mixed-valence compounds.