Impurity induced bound states and proximity effect in a bilayer exciton condensate

TL;DR

This paper investigates how impurities that cause local interlayer tunneling in bilayer exciton condensates create bound states and enhance interlayer coherence, potentially increasing the critical temperature for condensation.

Contribution

It introduces the concept of impurity-induced bound states in bilayer exciton condensates and links them to a proximity effect that boosts coherence and critical temperature.

Findings

Localized impurity states appear inside the gap for any impurity strength.

Impurity states enhance interlayer coherence around the impurity.

Finite impurity concentration can increase the critical temperature.

Abstract

The effect of impurities which induce local interlayer tunneling in bilayer exciton condensates is discussed. We show that a localized single fermion bound state emerges inside the gap for any strength of impurity scattering and calculate the dependence of the impurity state energy and wave function on the potential strength. We show that such an impurity induced single fermion state enhances the interlayer coherence around it, and is similar to the superconducting proximity effect. As a direct consequence of these single impurity states, we predict that a finite concentration of such impurities will increase the critical temperature for exciton condensation.