Effects of magnetic fields on the Datta-Das spin field-effect transistor

TL;DR

This paper investigates how magnetic fields and reservoir magnetizations influence spin and particle currents in a Datta-Das spin field-effect transistor with Rashba spin-orbit interaction, revealing conditions for optimal spin polarization control.

Contribution

It provides a detailed analysis of the effects of Zeeman fields and reservoir magnetizations on spin and particle currents, highlighting new ways to tune and enhance spin polarization in the device.

Findings

Spin currents into magnetized reservoirs are aligned with reservoir magnetization.

Spin current into unpolarized reservoirs can be tuned by magnetic fields and reservoir polarization.

Optimal spin polarization occurs with combined Zeeman fields and reservoir polarization.

Abstract

A Datta-Das spin field-effect transistor is built of a heterostructure with a Rashba spin-orbit interaction (SOI) at the interface (or quantum well) separating two possibly magnetized reservoirs. The particle and spin currents between the two reservoirs are driven by chemical potentials that are (possibly) different for each spin direction. These currents are also tuned by varying the strength of the SOI, which changes the amount of the rotation of the spins of electrons crossing the heterostructure. Here we investigate the dependence of these currents on additional Zeeman fields on the heterostructure and on variations of the reservoir magnetizations. In contrast to the particle current, the spin currents are not necessarily conserved; an additional spin polarization is injected into the reservoirs. If a reservoir has a finite (equilibrium) magnetization, then we surprisingly find that the spin current into that reservoir can only have spins which are parallel to the reservoir magnetization, independent of all the other fields. This spin current can be enhanced by increasing the magnetization of the other reservoir, and can also be tuned by the SOI and the various magnetic fields. When only one reservoir is magnetized then the spin current into the other reservoir has arbitrary tunable size and direction. In particular, this spin current changes as the magnetization of the other reservoir is rotated. The optimal conditions for accumulating spin polarization on an unpolarized reservoir are to either apply a Zeeman field in addition to the SOI, or to polarize the other reservoir.