Persistent Skyrmion Lattice of Noninteracting Electrons with Spin-Orbit Coupling

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., a = +/-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 noninteracting electron gas sustains a topologically nontrivial Skyrmion-lattice spindensity 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 noninteracting electrons.