Ballistic spin transport in exciton gases

TL;DR

This paper develops a theoretical framework for ballistic spin transport in exciton gases, highlighting how bosonic quasi-particles can carry spin coherently over long distances, offering an alternative to traditional electron-based spintronics.

Contribution

The paper introduces a comprehensive theory of exciton spin transport, including effects of spin-orbit interaction, magnetic fields, and exchange splittings, applicable to systems like GaAs/AlGaAs quantum wells.

Findings

Describes exciton spin dynamics influenced by spin-orbit and Zeeman effects.

Analyzes exciton transport in linear and nonlinear regimes.

Defines concepts of exciton spin current and spin conductivity.

Abstract

Traditional spintronics relies on spin transport by charge carriers, such as electrons in semiconductor crystals. This brings several complications: the Pauli principle prevents the carriers from moving with the same speed; Coulomb repulsion leads to rapid dephasing of electron flows. Spin-optronics is a valuable alternative to traditional spintronics. In spin-optronic devices the spin currents are carried by electrically neutral bosonic quasi-particles: excitons or exciton-polaritons. They can form highly coherent quantum liquids and carry spins over macroscopic distances. The price to pay is a finite life-time of the bosonic spin carriers. We present the theory of exciton ballistic spin transport which may be applied to a range of systems where bosonic spin transport has been reported, in particular, to indirect excitons in coupled GaAs/AlGaAs quantum wells. We describe the effect of spin-orbit interaction of electrons and holes on the exciton spin, account for the Zeeman effect induced by external magnetic fields, long range and short range exchange splittings of the exciton resonances. We also consider exciton transport in the non-linear regime and discuss the definitions of exciton spin current, polarization current and spin conductivity.