Emergence of the strong tunable linear Rashba spin-orbit coupling of two-dimensional hole gases in semiconductor quantum

TL;DR

This paper reveals a strong, tunable linear Rashba spin-orbit coupling in 2D hole gases within semiconductor quantum wells, challenging previous beliefs that it was purely cubic, and highlights Ge/Si quantum wells as promising for quantum computing.

Contribution

The study uncovers a significant linear Rashba SOC in 2DHG of semiconductor quantum wells, demonstrating its origin and potential for quantum applications, which was previously unrecognized.

Findings

Maximal Rashba SOC exceeds 120 meV·Å

Emergent SOC is a first-order direct Rashba effect

Ge-based 2DHG is promising for quantum computation

Abstract

Two-dimensional hole gases in semiconductor quantum wells are promising platforms for spintronics and quantum computation but suffer from the lack of the $\bf{k}$-linear term in the Rashba spin-orbit coupling (SOC), which is essential for spin manipulations without magnetism and commonly believed to be a $\bf{k}$-cubic term as the lowest order. Here, contrary to conventional wisdom, we uncover a strong and tunable $\bf{k}$-linear Rashba SOC in two-dimensional hole gases (2DHG) of semiconductor quantum wells by performing atomistic pseudopotential calculations combined with an effective Hamiltonian for a model system of Ge/Si quantum wells. Its maximal strength exceeds 120 meV{\AA}, comparable to the highest values reported in narrow bandgap III-V semiconductor 2D electron gases, which suffers from short spin lifetime due to the presence of nuclear spin. We also illustrate that this emergent $\bf{k}$-linear Rashba SOC is a first-order direct Rashba effect, originating from a combination of heavy-hole-light-hole mixing and direct dipolar intersubband coupling to the external electric field. These findings confirm Ge-based 2DHG to be an excellent platform towards large-scale quantum computation.