Paramagnetic contribution in superconductors with different-mass Cooper pairs

TL;DR

This paper reveals that superconductors with Cooper pairs of different effective masses exhibit paramagnetic contributions to superfluid stiffness, influenced by relative electron motion and particle-hole effects, offering new insights into unconventional superconductivity.

Contribution

It introduces the concept of paramagnetic contributions in superconductors with different-mass Cooper pairs, expanding understanding beyond traditional BCS theory.

Findings

Paramagnetic response arises from relative motion of electrons with different masses.

Particle-hole dichotomy effect is linked to mass differences in Cooper pairs.

Results provide new perspectives on electromagnetic response in unconventional superconductors.

Abstract

Cooper pairs formed by two electrons with different effective masses are common in multiband superconductors, pair density wave states, and other superconducting systems with multiple degrees of freedom. In this paper, we show that there are paramagnetic contributions to the superfluid stiffness in superconductors with different-mass Cooper pairs. This paramagnetic response is owing to the relative motion between two electrons with different mass. Additionally, we identify a particle-hole dichotomy effect related to this mass difference. We investigate the paramagnetic contributions based on the linear-response theory in two-band superconductors with interband pairings and in pair density wave states, respectively. Our results offer a different perspective of the electromagnetic superfluid stiffness in unconventional superconductors beyond the traditional BCS response.