Symmetry breaking for semiconductor excitons induced by Coulomb coupling between heavy and light holes

TL;DR

This paper investigates how Coulomb coupling between heavy and light holes affects exciton symmetry in semiconductors, revealing wave vector-dependent degeneracy splitting influenced by hole and electron masses.

Contribution

It introduces an optimized perturbative method to analyze exciton degeneracy breaking due to heavy-light hole coupling in zinc-blende semiconductors.

Findings

Degeneracy remains intact at zero wave vector.

Degeneracy splits into two branches at nonzero wave vector.

Splitting depends on heavy, light hole, and electron masses.

Abstract

Semiconductor excitons are commonly seen as hydrogen atom. This analogy requires a unique hole mass. In reality, this is not so due to the complexity of the semiconductor band structure. The precise consequences on the exciton physics of the Coulomb coupling between heavy and light holes remain a tricky open problem. Through an ``optimized perturbative'' approach that uses excitons with a flexible hole mass as a basis, we show that for zero exciton wave vector, the heavy-light hole mass difference does not split the $(2\times4)$ exciton degeneracy in zinc-blende-like semiconductors, the hole mass for binding energy being close to the average mass inverse. By contrast, for nonzero exciton wave vector, that physically breaks the crystal symmetry, the exciton degeneracy splits into two branches quantized along the exciton wave vector, with nontrivial center-of-mass dependence not only on the heavy and light hole masses, but also on the electron mass.