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.

中文翻译：

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冷冻机中的热量捕集：直接测量超导纳米线中的准粒子扩散

在超导体中非平衡准粒子的传播和松弛对于许多纳米级器件的功能，使其中一些器件能够运行以及限制其他器件的性能至关重要。加热到晶格温度以上的准粒子可能会通过声子或光子发射通道局部弛豫，或者在纳米结构中的适当距离内扩散，从而改变其远程组件的功能。由于其快速的动态性，在实时域中通过实验跟踪准粒子仍然是一项艰巨的任务。利用电子纳米温度计，基于探测超导纳米桥的温度相关开关电流，我们监测非平衡准粒子通量通过探测器时的热脉冲，其等效噪声温度为10$$千卡/$\sqrt{ñ}$，在哪里 $ñ$ 是探测电桥的脉冲数（通常是 $ñ=10000$），以及一纳秒的时间分辨率。测量提供了超导铝带中准粒子扩散的图像，并直接确定了扩散常数$d$ 等于100，cm${}^2$/ s，没有可见的能量依赖性。