An Exact SU(2) Symmetry and Persistent Spin Helix in a Spin-Orbit Coupled System

TL;DR

This paper discovers a new SU(2) spin rotation symmetry in specific spin-orbit coupled systems, leading to a Persistent Spin Helix with infinite spin lifetime, robust against disorder and interactions, and proposes experimental observation methods.

Contribution

It identifies a novel SU(2) symmetry in ReD and $[110]$ Dresselhauss models, enabling persistent spin textures and extending understanding of spin dynamics in these systems.

Findings

SU(2) symmetry exists in ReD and $[110]$ Dresselhauss models

Spin lifetime is infinite at the symmetry wavevector

Proposes experiments to observe the Persistent Spin Helix

Abstract

Spin-orbit coupled systems generally break the spin rotation symmetry. However, for a model with equal Rashba and Dresselhauss coupling constant (the ReD model), and for the $[110]$ Dresselhauss model, a new type of SU(2) spin rotation symmetry is discovered. This symmetry is robust against spin-independent disorder and interactions, and is generated by operators whose wavevector depends on the coupling strength. It renders the spin lifetime infinite at this wavevector, giving rise to a Persistent Spin Helix (PSH). We obtain the spin fluctuation dynamics at, and away, from the symmetry point, and suggest experiments to observe the PSH.