  The notion of a spin field effect transistor, where transistor action is
realized by manipulating the spin degree of freedom of charge carriers instead
of the charge degree of freedom, has captivated researchers for at least three
decades. These transistors are usually implemented by modulating the spin orbit
interaction in a two- or one-dimensional semiconductor structure with an
electrostatic potential, which then causes controlled spin precession in the
transistor's channel that modulates the current flowing between two
ferromagnetic (spin-polarized) source and drain contacts. Here, we introduce a
new concept for a spin field effect transistor whose channel is made of a
strained topological insulator
(strained-topological-insulator-field-effect-transistor or STI-SPINFET), which
does not exploit spin-orbit interaction. Instead, the transistor function is
elicited by straining the topological insulator (TI) with a gate voltage which
modifies the energy dispersion relation, or the Dirac velocity, to vary the
interference between the two spin eigenstates on the surface of the TI. This
modulates the current flowing between two ferromagnetic source and drain
contacts. The conductance on/off ratio of this transistor is too poor to be
useful as a switch, but it may have other uses, such as an extremely
energy-efficient stand-alone frequency multiplier.
