Influence of subband mixing, due to spin-orbit interaction, on the transmission through periodically modulated waveguides

Ballistic spin transport, through periodically stubbed waveguides, is studied in the presence of a weak spin-orbit interaction (SOI) and the resulting subband mixing. By an appropriate choice of the waveguide length and of the stub parameters injected spin-polarized electrons can be blocked completely and the transmission shows a periodic and nearly square-wave pattern with wide gaps when only one mode is allowed to propagate in the waveguide. Relative to the case when subband mixing is neglected, the transmission changes drastically as a function of the incident electron energy or of the stub height, as it exhibits new peaks or dips, but remains robust as a function of the stubs' degree of asymmetry. Varying the strength of the SOI parameter changes the relative contribution to the total transmission or conductance of the spin-up and spin-down states. The structure considered is a reasonable candidate for establishing a spin transistor.