Exotic interband pairing in multiband superconductors

TL;DR

This paper explores how interband pairing in multiband superconductors with spin-orbit coupling can exhibit unconventional features like triplet components and odd parity, affecting nodal structures and topologies.

Contribution

It reveals that interband pairing in tetragonal superconductors can display unconventional symmetry properties, altering nodal structures, which challenges traditional assumptions.

Findings

Interband pairing can have triplet components and odd parity.

Interband pairing influences the position and topology of nodal lines.

Conventional s-wave pairing can exhibit unconventional features due to spin-orbit coupling.

Abstract

Contrary to the usual assumption, the electron Bloch states in crystals with spin-orbit coupling do not always transform under symmetry operations in the same way as the pure spin-1/2 states. This has profound consequences for the symmetry properties and nodal structure of superconductors, especially for the interband gap functions. Focusing on tetragonal superconductors, we show that the interband pairing in the conventional (s-wave) channel can have features which are traditionally associated with unconventional pairing, such as triplet components and odd parity, and can produce line nodes in the excitation energy gap. In the d-wave case, the interband pairing, which can also be odd in momentum and have a triplet component, changes the positions and topology of the nodal lines.