Heat hunting in freezer: Direct measurement of quasiparticle diffusion in superconducting nanowire

TL;DR

This study introduces a real-time, high-resolution method to measure quasiparticle diffusion in superconducting nanostructures, revealing a diffusion constant of 100 cm²/s in aluminum without energy dependence.

Contribution

The paper presents a novel electronic nanothermometry technique for direct, real-time measurement of quasiparticle diffusion in superconductors, achieving nanosecond temporal resolution.

Findings

Measured quasiparticle diffusion constant D = 100 cm²/s in aluminum.

Achieved temperature sensitivity of 10 mK/√N with high temporal resolution.

Provided direct experimental visualization of quasiparticle diffusion dynamics.

Abstract

Propagation and relaxation of nonequilibrium quasiparticles in superconductors are of key importance for functioning of numerous nanoscale devices, enabling operation of some of them, and limiting the performance of the others. The quasiparticles heated above lattice temperature may relax locally via phonon or photon emission channels, or diffuse over appreciable distances in a nanostructure altering the functionality of their remote components. Tracing quasiparticles experimentally in real-time domain has remained the challenging task owing to their rapid dynamics. With electronic nanothermometry, based on probing of the temperature-dependent switching current of a superconducting nanobridge, we monitor heat pulse carried by a flux of nonequilibrium quasiparticles as it passes by our detector with a noise-equivalent temperature of $10\,$mK /$ \sqrt N$, where $N$ is the number of pulses probing the bridge (typically $N=10000$), and temporal resolution of a single nanosecond. The measurement provides the picture of quasiparticle diffusion in a superconducting aluminum strip and direct determination of the diffusion constant $D$ equal to $100$ cm$^2$/s with no energy dependence visible.