Effect of inter- and intra-subband spin–orbit interactions on the operation of a spin transistor with a double quantum well structure

Abstract

We consider electron transport in a Datta–Das spin transistor within the two-subband model taking into account intra- and inter-subband spin–orbit (SO) interactions, and study the influence of inter-subband SO coupling on the spin transistor operation. Starting from the model in which the SO coupling constants are treated as parameters, we show that the inter-subband SO interaction strongly affects the ordinary conductance oscillations predicted for the transistor with single occupancy. Interestingly, we find that even in the absence of the intra-subband SO interaction, the conductance oscillates as a function of the inter-subband SO coupling constant. This phenomenon is explained as resulting from the inter-subband transition with spin flip. Next, we consider the realistic spin transistor model based on the gated AlInAs/GaInAs double quantum well, for which the SO coupling constants are determined by the Schrödinger–Poisson approach. We show that the SO coupling constants rapidly change around Vg = 0, which is desirable for spin transistor operation. We demonstrate that for high electron densities the inter-subband SO interaction starts to play the dominant role. The strong evidence of this interaction is the reduction of the conductance for gate voltage Vg = 0, which leads to the reduction of the on/off conductance ratio.