Nonequilibrium Green's function approach to multi-band Cooper-pair transport: linear magnetoresistance effect due to nonunitary superconductivity

TL;DR

This paper develops a Green's function method to analyze multi-band Cooper-pair transport, revealing a linear magnetoresistance effect linked to nonunitary superconductivity, aiding detection of unconventional superconducting states.

Contribution

It introduces a novel formula for two-particle transmission in multi-band systems using a Green's function approach, bypassing traditional Andreev reflection assumptions.

Findings

Demonstrates a low-field linear magnetoresistance in nonunitary superconductors

Provides a direct calculation method for two-particle currents in multi-band systems

Suggests a new experimental route to detect unconventional superconductivity

Abstract

Many-body transport has emerged as an efficient tool for understanding interaction effects in quantum materials with a multi-band electronic structure. This paper proposes a formula for the two-particle transmission coefficient for Cooper-pair transport between multi-band normal and superconducting materials. The approach employs a tight-binding nonequilibrium Green's function technique, allowing a direct calculation of the two-particle current, without invoking the paradigm of Andreev reflection. As an application of the theory, we demonstrate a low-field linear magnetoresistance effect for superconductors with an induced nonunitary order parameter. These results uncover an unexplored route for detecting unconventional nonunitary superconductivity in quantum materials of current theoretical and experimental interest.