Dirac Semimetal Films as Spin Conductors on Topological Substrates

Spin-momentum locked states, notably those found on the surfaces of topological insulators, are promising for low-power electronic devices based on spin transport. Here we report a much more versatile case involving a Dirac semimetal film on a topological insulator substrate. Such a film can carry highly spin-polarized conduction channels by electronic coupling to the substrate. The spin channel width, defined by the film thickness, is at the designer's disposal, thus permitting optimization of the system parameters. The concept and underlying physics of such quasi-bulk spin channels are confirmed by calculations of a model system involving Bi$_{2}$Se$_{3}$ as the substrate and its low-Z substitute as the overlayer film. The results demonstrate Dirac semimetals as an important class of material for spintronic applications.