Crystal orientation dependence of the spin-orbit coupling in InAs nanowires

We compare the spin-orbit interaction (SOI) in InAs nanowires grown in the conventional $\ensuremath{\langle}0001\ensuremath{\rangle}$ crystal direction and the perpendicular $\ensuremath{\langle}01\overline{1}0\ensuremath{\rangle}$ direction. It is theoretically shown that, for individual transverse modes, the intrinsic contribution due to the bulk inversion asymmetry of the crystal vanishes for wires in the $\ensuremath{\langle}0001\ensuremath{\rangle}$ direction but remains finite for $\ensuremath{\langle}01\overline{1}0\ensuremath{\rangle}$. Experimental spin-orbit scattering lengths extracted from low-temperature magnetoresistance measurements of individual nanowires yields, however, comparable values in the two cases, suggesting that the intrinsic intramode spin-orbit term is not the dominant source of the SOI. We discuss the implications for the manipulation of SOI in nanowire devices.