Exceptional odd-frequency pairing in non-Hermitian superconducting systems

Jorge Cayao,Annica M Black-Schaffer

doi:10.1103/physrevb.105.094502

Abstract

We first show the realization of exceptional points in a non-Hermitian superconducting system based on a conventional superconductor and then demonstrate that, surprisingly, the system hosts odd-frequency pairing, solely generated by the non-Hermiticity. While there is a coexistence of even- and odd-frequency pairs under general conditions, we find that the even-frequency term vanishes at the exceptional degeneracies, leaving only odd-frequency pairing. This exceptional odd-frequency pairing is directly given by the imaginary part of the eigenvalues at the exceptional points and can be measured from the spectral function. Our results thus put forward non-Hermitian systems as a powerful platform to realize odd-frequency superconducting pairing.

Highlights

Superconductivity is a rare manifestation of quantum mechanics on a truly macroscopic scale and is a basic ingredient in emerging quantum technologies [1]
While the scheme for creating unconventional superconductors may differ, their properties are always to a very large extent dictated by the symmetries of their fundamental constituents, the electron, or Cooper, pairs
The connection between non-Hermiticity and odd-ω pairing has so far received little attention, with studies only focusing on symmetry classification [49] or spectral broadening in a Dynes superconductor [50]

Summary

INTRODUCTION

Superconductivity is a rare manifestation of quantum mechanics on a truly macroscopic scale and is a basic ingredient in emerging quantum technologies [1]. The connection between non-Hermiticity and odd-ω pairing has so far received little attention, with studies only focusing on symmetry classification [49] or spectral broadening in a Dynes superconductor [50]. This has left, for example, the role of the main NH characteristic, the EPs, completely unexplored. We find that all even-ω pairing vanishes at the EPs, leaving only a large odd-ω contribution, which we refer to as exceptional odd-ω pairing We illustrate these results in a realistic NH system consisting of a conventional superconductor coupled to a ferromagnet lead. Our findings put forward an entirely different route for generating odd-ω pairing, paving the way for NH engineering of dynamical superconducting states

PAIR AMPLITUDES

REALIZATION OF A NH SUPERCONDUCTING SYSTEM

EXCEPTIONAL ODD-ω PAIR AMPLITUDE

SPECTRAL SIGNATURES

CONCLUSIONS