Exact-diagonalization study of exciton condensation in electron bilayers

TL;DR

This study uses exact diagonalization to analyze exciton formation and condensation in electron bilayers, revealing a crossover from BCS-like pairing to Bose-Einstein condensation and effects of mass imbalance.

Contribution

It provides the first detailed exact-diagonalization analysis of exciton condensation in bilayer systems, highlighting the crossover behavior and influence of mass imbalance.

Findings

Demonstrates exciton formation as a prerequisite for phase coherence.

Identifies a crossover from BCS-like pairing to Bose-Einstein condensation.

Shows mass imbalance suppresses exciton condensation.

Abstract

We report on small-cluster exact-diagonalization calculations which prove the formation of electron-hole pairs (excitons) as prerequisite for spontaneous interlayer phase coherence in bilayer systems described by the extended Falicov-Kimball model. Evaluating the anomalous Green's function and momentum distribution function of the pairs, and thereby analyzing the dependence of the exciton binding energy, condensation amplitude, and coherence length on the Coulomb interaction strength, we demonstrate a crossover between a BCS-like electron-hole pairing transition and a Bose-Einstein condensation of tightly bound preformed excitons. We furthermore show that a mass imbalance between electrons and holes tends to suppress the condensation of excitons.