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\ifmmode^\circ\else\textdegree\fi{}K in the normal state and between 0.17 and 4.0\ifmmode^\circ\else\textdegree\fi{}K in the superconducting state. Within the experimental error the normal state heat capacity, ${C}_{n}$, can be represented by ${C}_{n}=\ensuremath{\gamma}T+\ensuremath{\beta}{T}^{3}$ with $\ensuremath{\gamma}=1.35\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ Joules/mole ${\mathrm{deg}}^{2}$ and a value of $\ensuremath{\beta}$ corresponding to a Debye temperature of 427.7\ifmmode^\circ\else\textdegree\fi{} 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 $\frac{{C}_{\mathrm{es}}}{\ensuremath{\gamma}{T}_{c}}=7.1\mathrm{exp}(\ensuremath{-}\frac{1.34{T}_{c}}{T})$, in which ${T}_{c}$ is the transition temperature, 1.163\ifmmode^\circ\else\textdegree\fi{}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\ifmmode^\circ\else\textdegree\fi{}K and shows a maximum negative deviation of 4% from the parabolic law. The results are compared with other measurements and with theory.

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