Excitonic instability and electric-field-induced phase transition towards a two dimensional exciton condensate

TL;DR

This paper investigates a 2D InAs-GaSb system where an electric field induces a sharp phase transition to an excitonic condensate, revealing a BCS-like gap and enabling exploration of the Bose-Einstein to BCS crossover.

Contribution

It demonstrates electric-field-induced excitonic phase transition in a 2D system with detailed calculations of the gap and transition characteristics.

Findings

A 3 meV BCS-like gap appears at the transition.

The transition is sharp and driven by exchange interaction.

External electric field controls exciton density and crossover.

Abstract

We present an InAs-GaSb-based system in which the electric-field tunability of its 2D energy gap implies a transition towards a thermodynamically stable excitonic condensed phase. Detailed calculations show a 3 meV BCS-like gap appearing in a second-order phase transition with electric field. We find this transition to be very sharp, solely due to exchange interaction, and so, the exciton binding energy is greatly renormalized even at small condensate densities. This density gradually increases with external field, thus enabling the direct probe of the Bose-Einstein to BCS crossover.