Spin currents in thermodynamic equilibrium: The challenge of discerning transport currents

Abstract

The standard definition of a spin current, applied to the conductors lacking inversion symmetry, results in nonzero spin currents. I demonstrate that the spin currents do not vanish even in thermodynamic equilibrium, in the absence of external fields. These currents are dissipationless and are not associated with real spin transport. The result should be taken as a warning indicating problems inherent in the theory of transport spin currents driven by external fields.