Intersubband spin-density excitations in quantum wells with Rashba spin splitting

TL;DR

This paper investigates how spin-orbit coupling and Rashba effects influence collective spin-density excitations in quantum wells, revealing that decoherence is mainly governed by many-body interactions rather than subband spin splitting.

Contribution

It introduces a density-functional formalism for analyzing intersubband spin-density excitations in spin-split quantum wells, highlighting the role of collective effects over single-particle spin splitting.

Findings

Coupling and wavevector-dependent splitting of SDEs observed.

Decoherence not primarily caused by subband spin splitting.

Dynamical exchange and correlation effects dominate decoherence.

Abstract

In inversion-asymmetric semiconductors, spin-orbit coupling induces a k-dependent spin splitting of valence and conduction bands, which is a well-known cause for spin decoherence in bulk and heterostructures. Manipulating nonequilibrium spin coherence in device applications thus requires understanding how valence and conduction band spin splitting affects carrier spin dynamics. This paper studies the relevance of this decoherence mechanism for collective intersubband spin-density excitations (SDEs) in quantum wells. A density-functional formalism for the linear spin-density matrix response is presented that describes SDEs in the conduction band of quantum wells with subbands that may be non-parabolic and spin-split due to bulk or structural inversion asymmetry (Rashba effect). As an example, we consider a 40 nm GaAs/AlGaAs quantum well, including Rashba spin splitting of the conduction subbands. We find a coupling and wavevector-dependent splitting of the longitudinal and transverse SDEs. However, decoherence of the SDEs is not determined by subband spin splitting, due to collective effects arising from dynamical exchange and correlation.