Specific Heat of Aluminum Near its Superconductive Transition Point

Abstract

We have carried out specific heat measurements with a high temperature—resolution in different magnetic fields on three cylindrical specimens of aluminum. The experiments were confined to the region of the critical field curve between 1.1 and 1.2°K and were carried out with a sensitive calorimeter in which temperature changes of ∼ 1.5 × 10-4 °K could be determined to about 2%. These measurements gave the difference of the specific heat between the superconductive and the normal state, the latent heat and the critical field curve. For a reversible transition, these three quantities are related by thermodynamic equations and hence it is possible to check their consistency. For one sample, this consistency was within experimental error and we obtained the slope (dHc/dT) H = 0= —153 gauss/degree. For the two other samples, there was some slight systematic disagreement between the critical curve as measured and as calculated. The shape of the transition in zero field has been investigated in detail and it was found that the phase change could take place within about 0.6 × 10-3°K for one sample, while for the two others it was spread over two millidegrees. From the width we have estimated the correlation range using Pippards theory. The critical temperatur in zero field was found to be respectively 1.173, 1.183 and 1.188°K and no λ anomaly in the specific heat, as discussed in recent theories could be detected at the transition.