Spatially-resolved probing of a non-equilibrium superconductor

TL;DR

This study experimentally investigates how non-equilibrium quasiparticles relax spatially in a superconductor at ultra-low temperatures, revealing effects on I-V characteristics influenced by temperature, current, and proximity.

Contribution

It provides the first spatially-resolved measurements of quasiparticle relaxation in superconductors, identifying two distinct length scales and confirming phenomenological models.

Findings

Quasiparticle injection modifies remote detector I-V characteristics.

Two length scales characterize charge and energy disequilibrium.

Results align with phenomenological models, highlighting the need for microscopic theory.

Abstract

Spatially resolved relaxation of non-equilibrium quasiparticles in a superconductor at ultra-low temperatures was experimentally studied. It was found that the quasiparticle injection through a tunnel junction results in modification of the shape of I-V characteristic of a remote `detector' junction. The effect depends on temperature, injection current and proximity to the injector. The phenomena can be understood in terms of creation of quasiparticle charge and energy disequilibrium characterized by two different length scales $\Lambda_{Q^{\ast}}$ $\sim5$ $\mu$m and $\Lambda_{T^{\ast}}\sim$ $40$ $\mu$m. The findings are in good agreement with existing phenomenological models, while more elaborated microscopic theory is mandatory for detailed quantitative comparison with experiment. The results are of fundamental importance for understanding electron transport phenomena in various nanoelectronic circuits.