Evidence for Two Time Scales in Long SNS Junctions

TL;DR

This study reveals two distinct time scales governing the critical and retrapping currents in long SNS Josephson junctions, linked to elastic and inelastic scattering processes, using microwave excitation across a broad frequency range.

Contribution

It demonstrates the presence of two separate dynamical regimes in long SNS junctions, associated with different scattering mechanisms, identified through frequency-dependent measurements.

Findings

Critical current is influenced by frequencies above the inverse diffusion time.

Retrapping current is affected by frequencies exceeding the electron-phonon rate.

Two different time scales correspond to elastic and inelastic scattering processes.

Abstract

We use microwave excitation to elucidate the dynamics of long superconductor / normal metal / superconductor Josephson junctions. By varying the excitation frequency in the range 10 MHz - 40 GHz, we observe that the critical and retrapping currents, deduced from the dc voltage vs. dc current characteristics of the junction, are set by two different time scales. The critical current increases when the ac frequency is larger than the inverse diffusion time in the normal metal, whereas the retrapping current is strongly modified when the excitation frequency is above the electron-phonon rate in the normal metal. Therefore the critical and retrapping currents are associated with elastic and inelastic scattering, respectively.