Current Induced Hotspot in Superconducting Thin Films with Different Thicknesses

Abstract

The temperature T_b dependence of current density j at the boundary of hotspot has been measured for granular aluminum thin films immersed in superfluid helium, whose temperature is T_b. The thickness d dependence of j-T_b characteristics, shows that the heat transfer from hotspot to superfluid helium, is almost limited by the thermal resistance between the electrons and lattice for thin films, d=14 and 28 nm. But, for a thicker film, d=112 nm, the Kapitza resistance must be considered in addition to the above thermal resistance.
Close to the superconducting transition temperature T_c, a finite region of T_b in which j is proportional to (T_c−T_b)^3⁄2, has been found. This characteristic is explained by theoretical results derived under the assumption that Joule heating depends not only on current density but also on temperature of the electrons.