Collective properties of indirect excitons in coupled quantum wells in random field

TL;DR

This paper investigates how random fields affect the superfluidity of indirect excitons in coupled quantum wells, deriving analytical expressions for collective excitations and superfluid properties, showing that disorder suppresses superfluidity.

Contribution

It provides analytical derivations of exciton Green's functions and superfluid parameters under strong random fields using CPA and Born approximations, extending understanding of disorder effects.

Findings

Superfluid density decreases with increasing random field.

Kosterlitz-Thouless transition temperature drops as disorder grows.

Analytical expressions for collective excitations are derived for different mass cases.

Abstract

The influence of a random field induced by impurities, boundary irregularities etc. on the superfluidity of a quasi-two-dimensional (2D) system of spatially indirect excitons in coupled quantum wells is studied. The interaction between excitons is taken into account in the ladder approximation. The random field is allowed to be large compared to the dipole-dipole repulsion between excitons. The coherent potential approximation (CPA) allows us to derive the exciton Green's function for a wide range of the random field, and the CPA results are used in the weak-scattering limit, which results in the second-order Born approximation. The Green's function of the collective excitations for the cases of (1) equal electron and hole masses and (2) the ``heavy hole'' limit are derived analytically. 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. This puts constraints on the experimental efforts to observe excitonic superfluidity.