Spin injection into a ballistic semiconductor microstructure

TL;DR

This paper develops a theory for spin injection in ballistic ferromagnet-semiconductor junctions, highlighting the role of Sharvin resistance and contact barriers in influencing spin injection efficiency.

Contribution

It provides explicit formulas for junction resistance and the spin-valve effect in ballistic regimes, advancing understanding of spin injection mechanisms.

Findings

Sharvin resistance suppresses spin injection in ballistic junctions

Contact barriers can enhance spin injection efficiency

Explicit formulas for junction resistance and spin-valve effect are derived

Abstract

A theory of spin injection across a ballistic ferromagnet-semiconductor-ferromagnet junction is developed for the Boltzmann regime. Spin injection coefficient $\gamma$ is suppressed by the Sharvin resistance of the semiconductor $r_N^*=(h/e^2)(\pi^2/S_N)$, where $S_N$ is the Fermi-surface cross-section. It competes with the diffusion resistances of the ferromagnets $r_F$, and $\gamma\sim r_F/r_N^*\ll 1$ in the absence of contact barriers. Efficient spin injection can be ensured by contact barriers. Explicit formulae for the junction resistance and the spin-valve effect are presented.