Low-Temperature Heat Capacities of Potassium, Rubidium, and Cesium

The heat capacities of potassium, rubidium, and cesium have been measured between 0.2 and 4.2^∘{}K. The thermal effective mass ratios are 1.25, 1.26, and 1.43, respectively. For potassium and rubidium these quantities are in reasonable agreement with theoretical estimates of the effects of band structure, electron-electron interactions, and electron-phonon interaction. The trends of the calculated and measured values suggest that the energy-band calculations overestimate the distortion of the Fermi surface in cesium. For potassium the elastic constants are known and can be compared with the observed T³ term in the lattice heat capacity. The agreement is within the expected experimental errors. The T⁵ term, however, does not agree with calculations based on a model that includes only first- and second-neighbor interactions.