Anomalous Surface Impedance in a Normal-metal/Superconductor Junction with a Spin-active Interface

TL;DR

This paper investigates how spin-active interfaces in normal-metal/superconductor junctions lead to unusual electromagnetic responses, including nonmonotonic temperature dependence and R>X in surface impedance, due to odd-frequency triplet Cooper pairs.

Contribution

It introduces the impact of spin-dependent potentials on surface impedance, revealing anomalous electromagnetic behavior caused by odd-frequency triplet pairing at the interface.

Findings

Surface impedance shows nonmonotonic temperature dependence.

Anomalous relation R>X observed at low temperatures.

Spin mixing induces odd-frequency triplet pairs affecting electromagnetic response.

Abstract

We discuss the surface impedance (Z=R-iX) of a normal-metal/superconductor proximity structure taking into account the spin-dependent potential at the junction interface. Because of the spin mixing transport at the interface, odd-frequency spin-triplet s-wave Cooper pairs penetrate into the normal metal and cause the anomalous response to electromagnetic fields. At low temperature, the local impedance at a surface of the normal metal shows the nonmonotonic temperature dependence and the anomalous relation R>X. We also discuss a possibility of observing such anomalous impedance in experiments.