Formal aspects of spin currents in material media

TL;DR

This paper explores the theoretical foundations of spin currents in various material media using relativistic and gauge theory techniques, revealing conditions for their conservation and defining an analogue photon spin current.

Contribution

It introduces a relativistic framework for spin currents in media, derives their governing equations from symmetries, and defines an analogue photon spin current, which are novel contributions.

Findings

Derived spin current equations from symmetry principles.

Identified conditions for spin current conservation.

Defined an analogue photon spin current.

Abstract

The relativistic generalization of the broken continuity equation that describes spin currents is exploited in general material media. The field theoretical techniques for the usual U(1) gauge theory with fermions in material media is employed. The spin current equations are obtained from the study of the symmetries of electrodynamics in material media. Moreover, we obtain the conditions that constrain the spin current to be conserved. One of the novel results is that the analogue spin current for the photon can be also defined. In the latter case, the conditions are useful constraints on the fields and the properties of the media.