Heat Hunting in a Freezer: Direct Measurement of Quasiparticle Diffusion in Superconducting Nanowire

Abstract

Propagation and relaxation of nonequilibrium quasiparticles in superconductors are fundamental for functioning of numerous nanoscale devices, enabling operation of some of them, and limiting the performance of 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 a 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/ √ N , where N is the number of pulses probing the bridge (typically N = 10 000), 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.

Quantum thermodynamics with a single superconducting vortex

“…4). The relaxation time in linear regime is 390 ns, in agreement with the thermal relaxation times for the aluminum nanowires studied by us in the earlier works, where either the switching of the nanobridge to the normal state (17) or the Joule heating of metallic island (15) was used to excite the QPs. The time is slightly smaller than expected from the electron-phonon relaxation channel alone due to the nonnegligible role of the QP diffusion along the leads and nonzero value of the magnetic field.…”

“…1F and Materials and Methods for details). Our approach is also compatible with time-resolved switching thermometry developed in recent years (15); therefore, we can measure the thermal response of the trap after applying a current pulse, which changes the vortex state of the box (figs. S3 to S5).…”

“…Mobile vortices become source of dissipation: Each moving vortex excites quasiparticles (QPs) along its trajectory ( 14 ). For fast electron-electron interaction, the presence of excess QPs is thermodynamically equivalent to the elevation of electron temperature ( 15 , 16 ).…”

Probing Confined Vortices with a Superconducting Nanobridge

“…We measure the switching current of the nanobridges in the dilution refrigerator at constant bath temperature of T 0 = 400 mK. We use the same measurement protocol like in our previous works [30,31]. The method is based on the testing of nanobridge with a train of N identical current pulses.…”

Heat Dissipation Mechanisms in Hybrid Superconductor–Semiconductor Devices Revealed by Joule Spectroscopy

“…Hybrid superconductor–semiconductor nanostructures have attracted great attention in the past decade as a platform for the development of novel quantum devices, , with focus on both topological Majorana fermions − and the study of conventional Andreev bound states, − among others. Additionally, of great interest are mesoscopic superconducting islands, comprised of tunnel-coupled isolated regions with finite charging energy, which have been used to define charge qubits , and to detect topological transitions − and are promising for building artificial Kitaev chains. − Common for these applications is a sensitivity to heightened temperature and nonequilibrium distributions of quasiparticles, which could introduce both quasiparticle (QP) poisoning and qubit decoherence. − The dynamics of such out-of-equilibrium QPs in superconductors, also referred to as “hot-electrons”, − are also responsible for the observed microcooling in SIN and SINIS devices, − interesting for the pursuit of nanoscale thermodynamic elements beyond their detrimental effects in quantum computation, and likely lie at the origin of the suppression of superconductivity by electrostatic gating in metallic films. ,, …”