How to utilize the Rashba effect in spin field effect transistor? The conventional nano-electronics are confronting many bottlenecks and spin-based devices have become the candidate for the next-generation nano-electronics (spintronics).
A semiconducting channel contacted with two ferromagnetic electrodes constitute a spin field effect transistor proposed by Datta and Das in $1990$, which is a fundamental device in spintronics, seeing the following schematic figure.

In the semiconductor channel, the Rashba effect will be employed to get a suitable spin precession angle or phase shift by spin-orbit coupling or gate voltage.
Here is my question: How to use the Rashba effect in the semiconductor channel to realize the on/off states of spin field effect transistor? What're the roles of spin-orbit coupling and gate voltage?
 A: In the proposal of Datta and Das, spin-polarized electrons enter the FET channel through the FM1 contact. These spin-polarized electrons are not in a spin-eigenstate of the two-dimensional electron gas. Therefore the spin starts to precess in the spin-orbit magnetic field intrinsic to the material as the electrons propagate. Once the electrons reach the opposite contact FM2, they will only be transmitted into this contact, if their resulting spin aligns with the orientation of the spin-polarized contact (low resistance state). In the opposite case they will be reflected (high resistance state).
The role of the gate voltage is to tune the electron density in the channel, and thereby the strength of the Rashba spin-orbit coupling, i.e. the strength of the intrinsic spin-orbit magnetic field. In this way, the precession frequency can be tuned, and, in theory, switching between the high and low resistance states can be achieved.
Rashba spin-orbit coupling is related to the structure inversion asymmetry of the channel in the direction normal to the channel plane. The gate voltage can increase or decrease the vertical electric fields causing the structure inversion asymmetry. A detailed description of this effect is nontrivial. It can be found in Roland Winkler's book on spin-orbit coupling effects in two-dimensional electron and hole systems.
Experimentally it has been shown, for example, by Nitta and Koga that the strength of the spin-orbit coupling can be tuned in an InGaAs-FET structure. To date a number of other experiments exist supporting this finding. An early review of the field of spintronics can be found here. Numerous more recent reviews can be readily found by an internet search.
