Evanescent states in 2D electron systems with spin-orbit interaction and spin-dependent transmission through a barrier

TL;DR

This paper studies evanescent electron states in 2D systems with spin-orbit interaction, revealing their impact on spin-dependent tunneling and polarization, including oscillatory effects and conditions for effective spin filtering.

Contribution

It identifies two types of evanescent states in 2D electron gases with spin-orbit coupling and analyzes their influence on spin-dependent transmission and polarization effects.

Findings

Evanescent states fill a gap in the spectrum with nonzero tangential momentum.

Transmission exhibits oscillatory dependence on barrier width and energy.

Unpolarized incident electrons can produce spin-polarized transmitted currents.

Abstract

We find that the total spectrum of electron states in a bounded 2D electron gas with spin-orbit interaction contains two types of evanescent states lying in different energy ranges. The first-type states fill in a gap, which opens in the band of propagating spin-splitted states if tangential momentum is nonzero. They are described by a pure imaginary wavevector. The states of second type lie in the forbidden band. They are described by a complex wavevector. These states give rise to unusual features of the electron transmission through a lateral potential barrier with spin-orbit interaction, such as an oscillatory dependence of the tunneling coefficient on the barrier width and electron energy. But of most interest is the spin polarization of an unpolarized incident electron flow. Particularly, the transmitted electron current acquires spin polarization even if the distribution function of incident electrons is symmetric with respect to the transverse momentum. The polarization efficiency is an oscillatory function of the barrier width. Spin filtering is most effective, if the Fermi energy is close to the barrier height.