Spin generation away from boundaries by nonlinear transport

TL;DR

This paper demonstrates how nonlinear transport effects can generate spin polarization deep within a sample, away from boundaries, through an analytically solvable model considering anisotropy and symmetry.

Contribution

It introduces a model showing spin accumulation from nonlinear effects and current gradients, extending understanding beyond boundary-proximate spin generation.

Findings

Nonlinear effects can generate spin polarization far from boundaries.

Isotropic conductivity with low symmetry geometry can produce spin polarization.

Drift from boundaries influences spin patterns observed in experiments.

Abstract

In several situations of interest, spin polarization may be generated far from the boundaries of a sample by nonlinear effects of an electric current, even when such a generation is forbidden by symmetry in the linear regime. We present an analytically solvable model where spin accumulation results from a combination of current gradients, nonlinearity, and cubic anisotropy. Further, we show that even with isotropic conductivity, nonlinear effects in a low symmetry geometry can generate spin polarization far away from boundaries. Finally, we find that drift from the boundaries results in spin polarization patterns that dominate in recent experiments on GaAs by Sih et al. [Phys. Rev. Lett. 97, 096605 (2006)].