Thermal nucleation of the normal state in superheated superconducting tin grains

Abstract

Suspensions of superheated type-I superconducting Sn microspheres of 16--25 and 10--25 \ensuremath{\mu}m diameters were irradiated at temperatures below 1 K and above 2 K by decay electrons from ${}^{14}\mathrm{C}$ and ${}^{35}\mathrm{S},$ respectively. Measurements of the radiation-induced gaps in the superheating transition curves indicate a full heating of the smallest grain volume of each suspension, contrary to a partial heating model based on the difference between quasiparticle relaxation and diffusion rates in Sn. The phonons are in thermal equilibrium with the quasiparticles when the normal state is nucleated.