Ab-initio calculations of spin tunneling through an indirect barrier

TL;DR

This paper employs ab-initio relativistic calculations to analyze spin tunneling through an indirect band gap barrier, revealing a strong dependence on in-plane momentum and identifying conditions for significant spin polarization.

Contribution

It introduces a fully relativistic ab-initio method for spin tunneling analysis and extends previous models by including in-plane momentum dependence.

Findings

Strong k_{||}-dependence of transmission and spin polarization

Identification of energy windows with 25-50% spin polarization

Spin polarization depends on transmission resonances, not spin splitting magnitude

Abstract

We use a fully relativistic layer Green's functions approach to investigate spin-dependent tunneling through a symmetric indirect band gap barrier like GaAs/AlAs/GaAs heterostructure along [100] direction. The method is based on Linear Muffin Tin Orbitals and it is within the Density Functional Theory (DFT) in the Local Density Approximation (LDA). We find that the results of our {\it ab-initio} calculations are in good agreement with the predictions of our previous empirical tight binding model [Phys. Rev. {\bf B}, 075313 (2006)]. In addition we show the $k_{||}$-dependence of the spin polarization which we did not previously include in the model. The {\it ab-initio} calculations indicate a strong $k_{||}$-dependence of the transmission and the spin polarization due to band non-parabolicity. A large window of 25-50 % spin polarization was found for a barrier of 8 AlAs monolayers at $k_{||}$ = 0.03 $2\pi/a$. Our calculations show clearly that the appearance of energy windows with significant spin polarization depends mostly on the location of transmission resonances and their corresponding zeros and not on the magnitude of the spin splitting in the barrier.