Spin transport in two‐dimensional hopping systems

An area of large current interest is the interplay of charge and spin transport of carriers in extended states. The study of this problem is of intrinsic scientific interest and is further motivated by the prospect of possible applications, e.g. a spin transistor. We perform a theoretical study of the interplay of charge and spin transport in the hopping regime. Specifically, we consider a two‐dimensional (2D) system with Rashba spin‐orbit interaction (SOI), where the localization of the electronic states is due to disorder and/or strong electron‐phonon interaction. In this case, the state description of each site contains the spin orientation in addition to the occupation number. As a first step, we solve the rate equations of these quantities for an ordered (polaronic) system in two‐site hopping approximation. Whereas the charge transport is not affected by SOI in this approximation, spin separation can occur if the crystal symmetry is sufficiently low. Furthermore, the total spin polarization normally decays exponentially. But, we find a critical threshold value for the in‐plane electrical field, above which the spin polarization oscillates. Thus, this comparably simple approximation already yields a surprisingly rich phenomenology. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)