Two-dimensional spin confinement in strained-layer quantum wells

We show that a two-dimensional spin system can occur for ‘‘heavy,’’ ${\mathit{m}}_{\mathit{J}}$=±3/2 holes resulting from a reduction to tetragonal symmetry produced by biaxial strain or confinement in a quantum well. Evidence is produced from magnetotransport measurements on strained ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{In}}_{\mathit{x}}$Sb/GaSb quantum wells, in which the spin splitting is determined only by the component of magnetic field in the growth direction, and from published work on unstrained GaAs/${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As heterojunctions. Complementary behavior is predicted for ‘‘light’’ holes.