Moving Stationary State of Exciton-Phonon Condensate in Cu2O

TL;DR

This paper presents a theoretical model for the moving Bose-Einstein condensate of para-excitons in Cu2O, incorporating exciton-phonon interactions and analyzing stability, collective excitations, and recent experimental interference phenomena.

Contribution

It introduces a new theoretical framework for exciton-phonon condensates in Cu2O, including moving inhomogeneous states and critical velocities, with applications to recent experimental observations.

Findings

Derived dynamic equations for exciton-phonon condensate

Identified two critical velocities for stability

Explained interference between coherent exciton-phonon packets

Abstract

We explore a simple theoretical model to describe the properties of Bose condensed para-excitons in Cu2O. Taking into account the exciton-phonon interaction and introducing a coherent phonon part of the moving condensate, we derive the dynamic equations for the exciton-phonon condensate. Within the Bose approximation for excitons, we discuss the conditions for the moving inhomogeneous condensate to appear in the crystal. We calculate the condensate wave function and energy and a collective excitation spectrum in the semiclassical approximation. The stability conditions of the moving condensate are analyzed by use of Landau arguments, and two critical velocities appear in the theory. Finally, we apply our model to describe the recently observed interference between two coherent exciton-phonon packets in Cu2O.