Heat Capacity of Aluminum between 0.1°K and 4.0°K

Measurements of the heat capacity of aluminum have been made between 0.11 and 4.0°K in the normal state and between 0.17 and 4.0°K in the superconducting state. Within the experimental error the normal state heat capacity, $C_n$, can be represented by $C_n=\gamma T+\beta T^3$ with $\gamma =1.35\mathrm{}\times {10}^{-3\mathrm{}}$ Joules/mole ${\mathrm{deg}}^2$ and a value of $\beta$ corresponding to a Debye temperature of 427.7° in agreement with calculations based on elastic constants. For reduced temperatures between 0.5 and 0.25 the electronic heat capacity in the superconducting state, $C_{\mathrm{es}}$, is approximated by $\frac{C_{\mathrm{es}}}{\gamma T_c}=7.1\mathrm{}\exp (-\frac{1.34T_c}{T})$, in which $T_c$ is the transition temperature, 1.163°K. At reduced temperatures less than about 0.25, $C_{\mathrm{es}}$ is greater than an extrapolation of the exponential, the difference amounting to a factor of 4 at the lowest temperature. The departure of $C_{\mathrm{es}}$ from an exponential temperature dependence, which is believed to be outside the experimental error, is not consistent with the existence of a constant energy gap at low reduced temperatures. The calculated critical field is 103.0 gauss at 0°K and shows a maximum negative deviation of 4% from the parabolic law. The results are compared with other measurements and with theory.