Dissipation and supercurrent fluctuations in a diffusive NS ring

TL;DR

This paper investigates the high-frequency response of a mesoscopic NS ring, revealing both dissipationless and dissipative supercurrent fluctuations, with dissipation mechanisms depending on frequency and temperature.

Contribution

It provides the first detailed measurement of high-frequency dissipation in a diffusive NS ring, distinguishing between different dissipation mechanisms related to Andreev states.

Findings

Dissipation includes both Josephson and dissipative components.

High-frequency dissipation arises from transitions above the minigap.

At lower frequencies, dissipation is mainly due to relaxation of Andreev state populations.

Abstract

A mesoscopic hybrid Normal/ Superconducting (NS) ring is characterized by a dense Andreev spectrum with a flux dependent minigap. We measure the linear response to a high frequency flux, in a wide frequency range, with a multimode superconducting resonator. We find that the current response contains, beside the well known dissipation-less Josephson contribution, a large dissipative component. At high frequency compared to the minigap and low temperature we find that the dissipation is due to transitions above the minigap. In contrast, at lower frequency there is range of temperature for which dissipation is caused predominantly by the relaxation of the Andreev states' population.