Electrical manipulation of spin-orbit coupling in semiconductor heterostructures

Spin-orbit coupling 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 semiconductor epilayers with strain\footnote{V. Sih, H. Knotz, J. Stephens, V. R. Horowitz, A. C. Gossard and D. D. Awschalom, \textit{Phys. Rev. B} \textbf{73}, 241316(R) (2006).} and in heterostructures using quantum confinement and orbital quantization\footnote{V. Sih, W. H. Lau, R. C. Myers, A. C. Gossard, M. E. Flatt\'{e} and D. D. Awschalom, \textit{Phys. Rev. B} \textbf{70}, 161313(R) (2004).}. These spin-splittings can provide a mechanism for electrically generating spin polarization without magnetic materials or magnetic fields. Using Kerr rotation microscopy, current-induced spin polarization and the spin Hall effect have been observed in bulk semiconductors and in a two-dimensional electron gas confined in (110) AlGaAs quantum wells\footnote{V. Sih, R. C. Myers, Y. K. Kato, W. H. Lau, A. C. Gossard and D. D. Awschalom, \textit{Nature Physics} \textbf{1}, 31 (2005).}. In contrast to measurements on bulk systems, the data for the quantum wells reveal that the spin Hall profile exhibits a complex structure and that the current-induced spin polarization is out-of-plane. The current-induced spin polarization is dependent on the direction along which the electric field is applied, reflecting the anisotropy of the spin-orbit interaction. More recently, we demonstrate that the observed spin accumulation due to the spin Hall effect is due to a bulk electron spin current\footnote{V. Sih, W. H. Lau, R. C. Myers, V. R. Horowitz, A. C. Gossard and D. D. Awschalom, \textit{Phys. Rev. Lett.} \textbf{97}, 096605 (2006).}. Channels with transverse arms allow us to observe that this spin current can drive spin transport over macroscopic distances in bulk GaAs.