A variational Monte Carlo study of exciton condensation

TL;DR

This paper investigates exciton condensation in a two-band Hubbard model using variational Monte Carlo, revealing a phase transition driven by interband Coulomb interaction and exploring the BCS-BEC crossover.

Contribution

It provides a detailed variational Monte Carlo analysis of exciton condensation, including phase transition mechanisms and exciton pairing characteristics.

Findings

Phase transition from excitonic to band insulator with increasing Coulomb interaction

Calculation of exciton pair amplitudes in momentum and real space

Discussion of BCS-BEC crossover within the excitonic insulator phase

Abstract

Exciton condensation in a two-band Hubbard model on a square lattice is studied with variational Monte Carlo method. We show that the phase transition from an excitonic insulator to a band insulator is induced by increasing the interband Coulomb interaction. To examine the character of the exciton condensation, the exciton pair amplitudes both in $\bm{k}$-space and in real space are calculated. Using these quantities, we discuss the BCS-BEC crossover within the excitonic insulator phase.