Non-local Tunneling Spectroscopy of Inelastic Quasiparticle Relaxation in Superconducting 1-D Wires

TL;DR

This study uses non-local tunneling spectroscopy on mesoscopic superconducting wires to analyze quasiparticle relaxation and energy imbalance, revealing pair-breaking effects and inelastic scattering times.

Contribution

It introduces a dual-bias scheme in non-local conductance experiments to extract quasiparticle energy imbalance effects in superconducting nanostructures.

Findings

Non-local conductance features due to pair-breaking are observed.

Energy-dependent inelastic scattering times are estimated from experimental data.

Kinetic effects of supercurrent are demonstrated and analyzed.

Abstract

Non-local conductance experiments using tunnel junctions can provide valuable spectroscopic information on both the transport and relaxation of quasiparticles in superconductors, as these techniques directly probe the quasiparticle charge and energy imbalance even at mK temperatures. In this work, we employ mesoscopic three terminal Cu and Al NIS devices to study non-local quasiparticle transport over length-scales on the order of the superconducting coherence length in this regime. Via a dual-bias scheme, which utilizes detector biases both above and below the superconducting gap, we are able to extract the effect of quasiparticle energy imbalance via its impact on the self consistent pair potential by symmetry considerations. We observe non-local conductance features due to pair-breaking which are anti-symmetric with respect to the polarity of the voltage bias, with a sharp onset during single electron tunneling at energies around $3\Delta$. We compare these findings with quasiclassical simulations including inelastic effects to obtain estimates of the energy dependent inelastic scattering time. In addition, we demonstrate kinetic effects due to a large applied supercurrent which can also be captured in this formalism and decomposed with respect to the particle-hole symmetry and supercurrent direction, and discuss further opportunities for the advancement of this method.