Current-induced spin polarization along spin orbit fields in strained InGaAs

Current-induced spin polarization is a phenomenon in which electron spins undergo a momentum-dependent net spin polarization \footnote{Y. K. Kato, R. C. Myers, A. C. Gossard, and D. D. Awschalom, Phys. Rev. Lett. {\bf93}, 176601 (2004)}, but the mechanism and how material parameters govern the magnitude of this effect remains an open question. Conductive channels are etched into strained n-doped InGaAs samples along the [110], [1$\overline{1}$0], [100] and [010] crystal axes with ohmic contacts at either end to allow control of electrical current. While the spin polarization direction is found to align along the direction of the measured spin-orbit effective magnetic fields \footnote{B. M. Norman, C. J. Trowbridge, J. Stephens, A. C. Gossard, D. D. Awschalom, and V. Sih, Phys. Rev. B. {\bf82}, 081304(R) (2010)}, the magnitude of the spin polarization is not proportional to the magnitude of the spin-orbit fields. Surprisingly, crystal axes with the smallest spin-orbit fields appear to have the largest net spin polarization. Our measurements suggest that the longer spin dephasing time for smaller spin-orbit interactions may play a significant role.