Mixed-parity superconductivity in centrosymmetric crystals

TL;DR

This paper develops a formalism for mixed-parity superconducting states in centrosymmetric crystals, revealing non-degenerate quasiparticle spectra, potential line nodes in the gap, and a predicted kink anomaly in muon spin relaxation.

Contribution

It introduces a weak-coupling approach to analyze mixed singlet-triplet superconductivity, including quasiparticle spectra and stability within Ginzburg-Landau theory, with applications to Pr(Os,Ru)4Sb12.

Findings

Quasiparticle energy spectrum can be non-degenerate despite unitary triplet component.

Superconducting gap may exhibit line nodes under strong spin-orbit coupling.

Predicted kink anomaly in muon spin relaxation rate at phase boundary.

Abstract

A weak-coupling formalism for superconducting states possessing both singlet (even parity) and triplet (odd parity) components of the order parameter in centrosymmetric crystals is developed. It is shown that the quasiparticle energy spectrum may be non-degenerate even if the triplet component is unitary. The superconducting gap of a mixed-parity state may have line nodes in the strong spin-orbit coupling limit. The pseudospin carried by the superconducting electrons is calculated, from which follows a prediction of a kink anomaly in the temperature dependence of muon spin relaxation rate. The anomaly occurs at the phase boundary between the bare triplet and mixed-parity states. The stability of mixed-parity states is discussed within Ginzburg-Landau theory. The results may have immediate application to the superconducting series Pr(Os,Ru)4Sb12.