Microwave Admittance of Gold-Palladium Nanowires with Proximity-Induced Superconductivity

TL;DR

This study measures the microwave admittance of gold-palladium SNS junctions at very low temperatures, revealing discrepancies between experimental results and existing theoretical models based on Usadel equations.

Contribution

It provides the first quantitative microwave admittance measurements of diffusive SNS junctions and compares them with theory, highlighting unresolved discrepancies.

Findings

Measured phase and temperature dependence of admittance near 1 GHz

Identified discrepancies between experimental data and Usadel theory

Revealed limitations of current theoretical models in describing microwave response

Abstract

We report quantitative electrical admittance measurements of diffusive superconductor--normal-metal--superconductor (SNS) junctions at gigahertz frequencies and millikelvin temperatures. The gold-palladium-based SNS junctions are arranged into a chain of superconducting quantum interference devices. The chain is coupled strongly to a multimode microwave resonator with a mode spacing of approximately 0.6 GHz. By measuring the resonance frequencies and quality factors of the resonator modes, we extract the dissipative and reactive parts of the admittance of the chain. We compare the phase and temperature dependence of the admittance near 1 GHz to theory based on the time-dependent Usadel equations. This comparison allows us to identify important discrepancies between theory and experiment that are not resolved by including inelastic scattering or elastic spin-flip scattering in the theory.