Content of review 1, reviewed on January 10, 2014
The Datta-Das transistor was proposed in 1990, and it has since become a quintessential example of a spintronic device. However, although various aspects of the Datta-Das transistor had been demonstrated, full realisation of such a device was absent in the literature prior to this paper. From a application perspective, much work would still need to be done to realise a device worthy of commercialisation (it operates at low cryogenic temperatures, and the signals are weak requiring operation in a non-local mode). Nevertheless the paper represents a breakthrough in demonstrating that complex spin manipulation can actually be achieved in real devices.
This paper describes the first experimental realisation of a Datta-Das transistor. Such a device requires injection of a spin-polarised current into a field-effect transistor structure. While traversing the channel of the transistor an applied gate voltage causes the spin to precess due to Rashba spin-orbit coupling (a non-inversion symmetric semiconductor must be used, in this case InAs). The drain electrode is ferromagnetic (as is the source electrode, in order to provide the spin polarised current). The spin polarised current can exit into the drain electrode only if the spin orientation is aligned with the magnetisation in the drain, and this will depend on the degree to which the spin orientation has precessed. The authors demonstrate an oscillating current as a function of gate voltage, and they demonstrate the absence of oscillations in control devices which strengthens their conclusion that they are observing the effect of spin precession. One key difference between their device and the original Datta-Das proposal is that they sense in a non-local fashion, i.e., the signal they measure is based on spin diffusion without actual current flow to the detection electrode. This reduces background signals. Overall, the work has been carried out in an excellent fashion and provides convincing evidence to support the authors' claims.
© 2014 the Reviewer (CC BY-SA 3.0).