SU(2)xU(1) unified theory for charge, orbit and spin currents

TL;DR

This paper develops a unified SU(2)×U(1) gauge theory framework to describe charge, orbit, and spin currents in spin-orbit coupled systems, revealing non-conservation and gauge field interactions.

Contribution

It introduces a novel unified gauge theory approach to spin and charge transport, incorporating Yang-Mills fields to explain spin torque and current dynamics.

Findings

Spin current non-conservation is balanced by SU(2) gauge contributions.

Orbit current is non-conserved under electromagnetic influence.

Yang-Mills fields induce forces on spin and spin current.

Abstract

Spin and charge currents in systems with Rashba or Dresselhaus spin-orbit couplings are formulated in a unified version of four-dimensional SU(2)$\times$U(1) gauge theory, with U(1) the Maxwell field and SU(2) the Yang-Mills field. While the bare spin current is non-conserved, it is compensated by a contribution from the SU(2) gauge field, which gives rise to a spin torque in the spin transport, consistent with the semi-classical theory of Culcer et al. Orbit current is shown to be non-conserved in the presence of electromagnetic fields. Similar to the Maxwell field inducing forces on charge and charge current, we derive forces acting on spin and spin current induced by the Yang Mills fields such as the Rashba and Dresselhaus fields and the sheer strain field. The spin density and spin current may be considered as a source generating Yang-Mills field in certain condensed matter systems.