On Critical Velocities in Exciton Superfluidity

TL;DR

This paper investigates how exciton-phonon interactions influence superfluidity, revealing two critical velocities that determine the existence of exciton condensates as bright solitons, supported by derived spectra and wave equations.

Contribution

It introduces a novel analysis of critical velocities in exciton superfluidity considering exciton-phonon interactions using the Landau criterion.

Findings

Identification of two critical velocities for exciton superfluidity.

Existence of bright solitons within specific velocity ranges.

Derivation of excitation spectrum and wave function equations.

Abstract

The presence of exciton phonon interactions is shown to play a key role in the exciton superfluidity. We apply the Landau criterion for an exciton-phonon condensate moving uniformly at zero temperature. It turns out that there are essentially two critical velocities in the theory. Within the range of these velocities the condensate can exist only as a bright soliton. The excitation spectrum and differential equations for the wave function of this condensate are derived.