Energy-transport phenomena in single superconducting grains

Superheated, superconducting grains have been proposed as detectors for dark matter and low-energy neutrinos. We present measurements with irradiation by monoenergetic α particles on single In and Sn grains at ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ temperatures. A local-heating model which explains the structure of our data is developed. The difference between local heating and global heating (seen previously for Al and Zn) is explained by the different rates of quasiparticle relaxation in these materials. There are indications that the phonons have not reached thermal equilibrium with the quasiparticles when the grain flips.