Probing thermalization and dynamics of high-energy quasiparticles in a superconducting nanowire by scanning critical current microscopy

TL;DR

This study uses scanning critical current microscopy to investigate how high-energy quasiparticles affect superconducting nanowires, revealing thermal mechanisms and rapid hot spot dynamics crucial for device optimization.

Contribution

It introduces a method to independently control quasiparticle energy and injection rate, providing new insights into the thermal dynamics in superconducting nanostructures.

Findings

Critical current reduction is mainly driven by injected power.

Thermal mechanisms dominate the critical current suppression.

Hot spot dynamics occur rapidly after quasiparticle injection.

Abstract

Besides its fundamental interest, understanding the dynamics of pair breaking in superconducting nanostructures is a central issue to optimize the performances of superconducting devices such as qubits or photon detectors. However, despite substantial research efforts, these dynamics are still not well understood as this requires experiments in which quasiparticles are injected in a controlled fashion. Until now, such experiments have employed solid-state tunnel junctions with a fixed tunnel barrier. Here we use instead a cryogenic scanning tunnelling microscope to tune independently the energy and the rate of quasiparticle injection through, respectively, the bias voltage and the tunnelling current. For high energy quasiparticles, we observe the reduction of the critical current of a nanowire and show it is mainly controlled by the injected power and, marginally, by the injection rate. Our results prove a thermal mechanism for the reduction of the critical current and unveil the rapid dynamics of the generated hot spot.