Symmetry analysis of odd- and even-frequency superconducting gap symmetries for time-reversal symmetric interactions

TL;DR

This paper uses group theory to analyze how both even- and odd-frequency superconducting gaps can exist under time-reversal symmetric interactions, expanding the classification of superconducting states.

Contribution

It introduces a group theoretical framework based on Shubnikov groups to classify odd- and even-frequency superconducting gap symmetries, including specific lattice examples.

Findings

Both even- and odd-frequency gaps are allowed under time-reversal symmetric interactions.

Revealed the combinations of s-, d-, and p-wave gaps for different symmetry representations.

Constructed a generalized Ginzburg-Landau theory for these symmetries.

Abstract

Odd-frequency superconductivity describes a class of superconducting states where the superconducting gap is an odd function in relative time and Matsubara frequency. We present a group theoretical analysis based on the linearized gap equation in terms of Shubnikov groups of the second kind. By discussing systems with spin-orbit coupling and an interaction kernel which is symmetric under the reversal of relative time, we show that both even- and odd-frequency gaps are allowed to occur. Specific examples are discussed for the square lattice, the octahedral lattice, and the tetragonal lattice. For irreducible representations that are even under reversal of relative time the common combinations of $s$- and d-wave spin singlet and p-wave spin triplet gaps are revealed, irreducible representations that are odd under reversal of relative time give rise to $s$- and d-wave spin triplet and p-wave spin singlet gaps. Furthermore, we discuss the construction of a generalized Ginzburg-Landau theory in terms of the associated irreducible representations. The result complements the established classification of superconducting states of matter.