Thermal Conductivity of Indium-Thallium Alloys in the Normal and Superconducting States

Thermal conductivity measurements have been made on three indium-thallium alloys between 0.15° and 0.8°K. Temperature gradients were measured using carbon resistance thermometers. The alloys were of the type which show an increase in thermal conductivity on entering the superconducting state. At temperatures below 1°K the superconducting state thermal conductivity decreases rapidly with decreasing temperature, becoming roughly proportional to $T^3$ and to the grain size in the specimens at the lowest temperatures. The data are interpreted as meaning that phonon conductivity limited by boundary scattering is important in this region.