Measurements of the temperature dependence of the heat capacity of granular aluminum films have been carried out using ac calorimetry. The results indicate a peak in the heat capacity at the low.
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In this letter we report measurements of the temperature dependence of the heat capacity of 1000-A granular aluminum films using an ac measuring technique \[1\ ]. Films deposited on cleaved mica substrates were heated optically at 1 kHz, and as suggested by Ferrell \[2\],t he experimental resistance-temperature characteristic of the superconducting transition was used as a thermometer. The results in nine films indicate a rise in the heat capacity near the low-temperature end of the resistive transition. In two samples the electrical resistance at the low-temperature end of the transition was large enough to provide thermometry accurate enough to establish the existence of a peak. These measurements should be contrasted with the monotonic variation of the heat capacity with temperature found by Zally and Mochel \[3\]i n Bi0.37Sb0.63 films. The lower limit for the heights of the peaks of the two samples was more than ten times the BCS jump \[4\].T he peaks, which were 2 to 3 mK wide, occured at temperatures which were 20 mK and 50 mK below transition temperatures determined by fits to the conductivity data \[5\].T he entropy under the peaks was estimated to be between 1 and 5% of the entropy in the electronic system at T c. More precise limits could not be determined because of an uncertainly in the magnitude of the background contribution to the heat capacity. The heat capacity at a particular temperature was Supported in part by the U.S. Atomic Energy Commission under contract AT( 11 - 1 )-1569 and by the Graduate School of the University of Minnesota. * Present address: Stanford Research Institute, Menlo Park, California 94025.
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