Persistent Skyrmion Lattice of Noninteracting Electrons with Spin-Orbit Coupling

TL;DR

This paper predicts a topologically non-trivial skyrmion lattice in non-interacting 2D electron gases with tuned Rashba and Dresselhaus spin-orbit couplings, enabling potential observation of topological effects in GaAs wells.

Contribution

It introduces the concept of a Persistent Skyrmion Lattice formed from crossed persistent spin helices in non-interacting electrons with tunable spin-orbit couplings.

Findings

Skyrmion lattice persists with balanced Rashba and Dresselhaus couplings.

Robustness against disorder and interactions demonstrated.

Spin relaxation rate comparable to cubic Dresselhaus term.

Abstract

A persistent spin helix (PSH) is a robust helical spin-density pattern arising in disordered 2D electron gases with Rashba $\alpha$ and Dresselhaus $\beta$ spin-orbit (SO) tuned couplings, i.e., $\alpha=\pm\beta$. Here we investigate the emergence of a Persistent Skyrmion Lattice (PSL) resulting from the coherent superposition of PSHs along orthogonal directions -- crossed PSHs -- in wells with two occupied subbands $\nu=1,2$. For realistic GaAs wells we show that the Rashba $\alpha_\nu$ and Dresselhaus $\beta_\nu$ couplings can be simultaneously tuned to equal strengths but opposite signs, e.g., $\alpha_1= \beta_1$ and $\alpha_2=-\beta_2$. In this regime and away from band anticrossings, our {\it non-interacting} electron gas sustains a topologically non-trivial skyrmion-lattice spin-density excitation, which inherits the robustness against spin-independent disorder and interactions from its underlying crossed PSHs. We find that the spin relaxation rate due to the interband SO coupling is comparable to that of the cubic Dresselhaus term as a mechanism of the PSL decay. Near anticrossings, the interband-induced spin mixing leads to unusual spin textures along the energy contours beyond those of the Rahsba-Dresselhaus bands. Our PSL opens up the unique possibility of observing topological phenomena, e.g., topological and skyrmion Hall effects, in ordinary GaAs wells with non-interacting electrons.