Exciton mass and exciton spectrum in the cuprous oxide

TL;DR

This paper introduces a lattice model to analyze exciton properties in cuprous oxide, capturing effects of strong central-cell corrections, non-parabolic band structure, and short-range interactions, revealing exciton mass enhancement and anisotropy.

Contribution

The study presents a novel lattice-based approach that models the crossover from Wannier to Frenkel excitons, incorporating complex band and interaction effects specific to cuprous oxide.

Findings

Predicted strongly anisotropic ortho-exciton mass.

Reproduced optical spectrum deviations from hydrogen-like series.

Quantified exciton mass enhancement due to central-cell effects.

Abstract

Excitons with a radius of a few lattice constants can be affected by strong central-cell corrections, leading to significant deviations of the optical spectrum from the hydrogen-like Rydberg series, and also to an enhancement of the exciton mass. We present an approach to this situation based on a lattice model that incorporates the effects of a non-parabolic band structure, short distance corrections to the Coulomb interaction between electrons and holes, spin-orbit and exchange coupling. The lattice model allows for observation of the crossover from large radius Wannier to small radius Frenkel excitons without invoking a continuum approximation. We apply the lattice model approach especially to the yellow exciton series in the cuprous oxide, for which the optical spectrum and exciton mass enhancement are obtained through adaptation of only a few model parameters to material-specific values. Our results predict a strongly anisotropic ortho-exciton mass.