Thermal Bottleneck in a Freely Suspended Superconducting Island on InAs Nanowire

We investigate the heat balance in superconducting islands (S-islands) formed in epitaxial Al/InAs nanowires freely suspended above the substrate. We employ a Joule spectroscopy approach, which traces the superconductor-normal transition in the S-island mediated by heating of the neighboring InAs nanowire segments via transport current. The temperature of the surrounding 3 He bath is varied with nearby mesoscopic heaters and controlled with the NW Johnson noise thermometry. The experiment reveals a substantial thermal relaxation bottleneck associated with the cooling via surrounding 3 He, which gives rise to phonon heating in the S‑island. Our results uncover the role of environmental cooling in non-equilibrium experiments in S-islands in in nanowire devices.