Quasi-equilibrium optical nonlinearities in spin-polarized GaAs

TL;DR

This paper extends the microscopic modeling of optical nonlinearities in GaAs to include spin polarization, accounting for many-body effects and matching experimental observations of spin-dependent absorption.

Contribution

It introduces a modified Bethe-Salpeter equation solution that incorporates spin polarization and light holes in a three-band model for GaAs.

Findings

Reproduces spin-dependent absorption trends in GaAs at room temperature.

Accounts for density-dependent and spectral effects in spin-polarized optical absorption.

Provides a tool for microscopic modeling of nonlinearities in spin-polarized semiconductors.

Abstract

Semiconductor Bloch equations, which microscopically describe the dynamics of a Coulomb interacting, spin-unpolarized electron-hole plasma, can be solved in two limits: the coherent and the quasi-equilibrium regime. These equations have been recently extended to include the spin degree of freedom, and used to explain spin dynamics in the coherent regime. In the quasi-equilibrium limit, one solves the Bethe-Salpeter equation in a two-band model to describe how optical absorption is affected by Coulomb interactions within a spin-unpolarized plasma of arbitrary density. In this work, we modified the solution of the Bethe-Salpeter equation to include spin-polarization and light holes in a three-band model, which allowed us to account for spin-polarized versions of many-body effects in absorption. The calculated absorption reproduced the spin-dependent, density-dependent and spectral trends observed in bulk GaAs at room temperature, in a recent pump-probe experiment with circularly polarized light. Hence our results may be useful in the microscopic modelling of density-dependent optical nonlinearities in spin-polarized semiconductors.