Exciton-phonon interaction breaking all antiunitary symmetries in external magnetic fields

TL;DR

This paper demonstrates that exciton-phonon interactions induce Gaussian unitary ensemble (GUE) statistics in magnetoexcitons regardless of magnetic field orientation, explaining experimental results that previous models could not.

Contribution

It shows that exciton-phonon interactions combined with the cubic lattice break all antiunitary symmetries, leading to GUE statistics for magnetoexcitons in any magnetic field orientation.

Findings

Exciton-phonon interactions induce GUE statistics for all field orientations.

Breaking all antiunitary symmetries requires both exciton-phonon interaction and cubic lattice effects.

The model aligns with experimental observations of magnetoexcitons in cuprous oxide.

Abstract

Recent experimental investigations by M. A{\ss}mann et al. [Nature Mater. 15, 741 (2016)] on the spectrum of magnetoexcitons in cuprous oxide revealed the statistics of a Gaussian unitary ensemble (GUE). The model of F. Schweiner et al. [Phys. Rev. Lett. 118, 046401 (2017)], which includes the complete cubic valence band structure of the solid, can explain the appearance of GUE statistics if the magnetic field is not oriented in one of the symmetry planes of the cubic lattice. However, it cannot explain the experimental observation of GUE statistics for all orientations of the field. In this paper we investigate the effect of quasi-particle interactions or especially the exciton-phonon interaction on the level statistics of magnetoexcitons and show that the motional Stark field induced by the exciton-phonon interaction leads to the occurrence of GUE statistics for arbitrary orientations of the magnetic field in agreement with experimental observations. Importantly, the breaking of all antiunitary symmetries can be explained only by considering both the exciton-phonon interaction and the cubic crystal lattice.