Phase transitions in a system of indirect magnetoexcitons in coupled quantum wells at high magnetic field: the role of disorder

TL;DR

This paper investigates how disorder and high magnetic fields affect the phase transitions and superfluid properties of a 2D system of indirect magnetoexcitons in coupled quantum wells, revealing a quantum transition to superfluidity at zero temperature.

Contribution

It develops an effective Hamiltonian for magnetoexcitons in disorder and high magnetic fields, analyzing the suppression of superfluidity and the quantum phase transition in this system.

Findings

Increasing magnetic field and interwell distance raises disorder effects.

Disorder suppresses superfluid density and transition temperature.

Quantum phase transition to superfluidity occurs at zero temperature depending on magnetic field and disorder.

Abstract

Collective properties of a quasi-two-dimensional (2D) system of spatially indirect magnetoexcitons in coupled quantum wells (CQW) in high magnetic field $H$ were analyzed in the presence of disorder. The Hamiltonian of the dilute gas of magnetoexcitons with dipole-dipole repulsion in a random field has been reduced to the Hamiltonian of a dilute gas of dipolar excitons without an applied magnetic field, but in an $H$-dependent effective random field and having an effective mass of magnetoexciton which is a function of the magnetic field and parameters of the CQW. For 2D magnetoexcitonic systems, the increase of the magnetic field $H$ and the interwell distance $D$ is found to increase the effective renormalized random field parameter $Q$ and suppress the superfluid density $n_s$ and the temperature of the Kosterlitz-Thouless transition $T_c$. It is shown that in the presence of the disorder there is a quantum transition to the superfluid state at zero temperature T=0 with respect to the magnetic field $H$ and the parameters of the disorder. There is no superfluidity at any exciton density in the presence of the disorder at sufficiently large magnetic field $H$ or sufficiently large disorder.