Superfluidity of "dirty" indirect excitons in coupled quantum wells

TL;DR

This paper investigates how disorder affects superfluidity in two-dimensional excitons within coupled quantum wells, revealing that increasing randomness diminishes superfluid density and transition temperature.

Contribution

It provides a theoretical analysis of superfluidity in disordered excitonic systems, applying the CPA method to derive Green's functions and phase transition parameters.

Findings

Superfluid density decreases with increasing disorder.

Kosterlitz-Thouless transition temperature drops as randomness grows.

Theoretical framework applicable to experimental excitonic systems.

Abstract

The theory of what happens to a superfluid in a random field, known as the ``dirty boson'' problem, directly relates to a real experimental system presently under study by several groups, namely excitons in coupled semiconductor quantum wells. We consider the case of bosons in two dimensions in a random field, when the random field can be large compared to the repulsive exciton-exciton interaction energy, but is small compared to the exciton binding energy. The interaction between excitons is taken into account in the ladder approximation. The coherent potential approximation allows us to derive the exciton Green's function for a wide range of the random field strength, and in the weak-scattering limit CPA results in the second-order Born approximation. For quasi-two-dimensional excitonic systems, the density of the superfluid component and the Kosterlitz-Thouless temperature of the superfluid phase transition are obtained, and are found to decrease as the random field increases.