Electrical manipulation of spin-orbit coupling in semiconductor heterostructures

Spin-orbit coupling in semiconductors relates the spin of an electron to its momentum and provides a pathway for electrically initializing and manipulating electron spins. This coupling creates momentum-dependent spin-splittings related to the inversion asymmetries of the semiconductor heterostructure. We demonstrate that we can regulate these spin-splittings in bulk semiconductor epilayers with strain and in semiconductor heterostructures using quantum confinement and orbital quantization. Using spatially- and time-resolved optical spectroscopy, we can map these spin-splittings and observe their effects on the electron spin dynamics. In addition, we study electrically-generated spin polarization in bulk semiconductors and quantum wells. Measurements of the spin Hall effect in a two-dimensional electron gas confined in (110) AlGaAs quantum wells reveal a complex structure to the spin accumulation, which is in contrast to measurements on bulk epilayers. In addition, the current-induced spin polarization for the (110) quantum wells is oriented out-of-plane. The experiments map the strong dependence of the current-induced spin polarization to the crystal axis along which the electric field is applied, reflecting the anisotropy of the spin-orbit interaction. Finally, we have performed measurements of the spin Hall effect in structures patterned on GaAs epilayers that allow us to separate the effects of the sample boundary from the boundary of the electric field. These channels with transverse arms allow us to determine that the spin Hall effect produces a transverse bulk spin current and that this spin current can drive spin transport over macroscopic distances in bulk GaAs.