Spin-Transistor Action via Tunable Landau-Zener Transitions

A Different Spin Transistor A typical transistor consists of a source and a drain; the current that makes it to the drain is controlled by applying voltage to the third terminal, called the gate. In spin-based electronics, where spin current is used instead of charge, the source and the drain are ferromagnetic materials connected by a narrow semiconducting channel. This design, however, suffers from low efficiency. Betthausen et al. (p. 324; see the Perspective by Žutić and Lee) combined homogeneous and helical magnetic fields to change the orientation of the spin on its way to the drain, preserving spin information over distances many times the spin mean free path. The transistor is “on” when the transport is adiabatic—i.e., slow enough for the spin to be able to adapt to the local magnetic field—and “off” otherwise. An alternative design for a spin-based transistor proves tolerant to disorder. Spin-transistor designs relying on spin-orbit interaction suffer from low signal levels resulting from low spin-injection efficiency and fast spin decay. Here, we present an alternative approach in which spin information is protected by propagating this information adiabatically. We demonstrate the validity of our approach in a cadmium manganese telluride diluted magnetic semiconductor quantum well structure in which efficient spin transport is observed over device distances of 50 micrometers. The device is turned “off” by introducing diabatic Landau-Zener transitions that lead to a backscattering of spins, which are controlled by a combination of a helical and a homogeneous magnetic field. In contrast to other spin-transistor designs, we find that our concept is tolerant against disorder.