Normal-state electronic and lattice specific heats of Pb-In alloys below 8 K

New measurements of the γ values for disordered Pb-In alloys are presented, which differ appreciably from previously reported data, and which contradict the conclusion that the rigid-band model holds for a very wide range of concentrations. The disagreement is shown to stem from a failure to take into account deviations of the very-low-temperature lattice specific heat from the expected T³ law. In particular, the lattice contribution can be described in terms of an effective Debye temperature which increases with T near absolute zero, for sufficiently large indium concentrations. An analysis based on the specific-heat and entropy differences between normal and superconducting states is described, which avoids the errors likely to arise using the traditional procedure in such cases.