Spin injection using quantum point contacts with spin-orbit interaction and its detection

We propose a spin-injection method utilizing quantum point contacts (QPCs) fabricated on narrow-gap semiconductors with strong Rashba spin-orbit (SO) interaction. When the conductance through a QPC is quantized in units of 2e(2)/h, the current is spin-polarized in the transverse direction to the current even in the absence of magnetic field. The spin polarization, which would be larger than 50% in InGaAs heterostructures, can be detected by connecting the QPC to a ferromagnetic lead. Then the conductance is maximal (minimal) when the magnetization in the lead is parallel or antiparallel (perpendicular) to the spin polarization of the current. The same conductance in the parallel and antiparallel alignments is explained by the Onsager relation, reflecting the fact that the SO interaction does not break the time reversal symmetry. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.