Spin-split Fermi surfaces and helical spin winding in a 2DEG heterostructure
Rashba SOC (H_R = α(k×σ)·ẑ) splits the 2DEG into two spin-helical Fermi circles. Dresselhaus SOC (H_D = β(kₓσₓ − k_yσ_y)) has a different spin texture. When α = β, a persistent spin helix emerges with SU(2) symmetry — spin lifetime diverges. The spin expectation on the Fermi surface winds as ⟨σ⟩ = ±(−sin φ, cos φ, 0) for pure Rashba.