  The Datta-Das-type spin field-effect transistor, using a two-dimensional
electron gas in a semiconductor heterostructure as a channel, plays a key role
in spintronics. Here, we theoretically present a type of spin field-effect
transistor based on massless birefringent Dirac fermions in polar Dirac
semimetals. The manipulation of spin arises from the existence of the strong
spin-orbit coupling, polar space groups, and Dirac cones in a single phase. The
oscillatory channel conductance can be controlled by the sign of gate voltage
in addition to its magnitude due to the gapless band structures of polar Dirac
semimetals. Such spin field-effect transistor provides guidance for the further
design of spintronic devices.
