A Singlet-pairing superconductor is always also a super-spin-current-conductor

TL;DR

The paper demonstrates that singlet-pairing superconductors can sustain dissipation-less spin currents without losing their superconducting properties, maintaining their thermodynamic and universal characteristics.

Contribution

It shows that singlet superconductors can carry persistent spin currents without depairing, extending the understanding of superconductor spin transport.

Findings

Singlet pairing remains effective with moderate spin currents.

Superconductors stay fully gapped and thermodynamically similar with spin currents.

Universal relations of BCS theory remain valid with spin currents.

Abstract

It is shown that, in a conductor carrying a moderate spin current, singlet pairing can still take place almost as effectively as without a spin current. The system will still be fully gapped for all spin-up and -down single-particle excitations, with no depaired electrons. All thermodynamic properties will be practically the same as without the spin current. All universality relations and laws of corresponding states found in the theory of Bardeen, Cooper, and Schrieffer should remain valid. Thus a singlet-pairing superconductor can always carry a persistent and dissipation-less spin-current. A heuristic argument to support this conclusion is also given, as well as two possible experimental tests of this prediction.