The thermal and electrical conductivity of sodium at low temperatures

Modem theories of metallic conduction, based on the quantum interaction of electrons with the lattice vibrations, predict a considerable variation of Lorenz number with temperature. We have carried out measurements of the thermal and electrical conductivity of two rather pure specimens of sodium continuously from 90 to ~ 4° K and derived an experimental Lorenz curve. Considerable deviations from theory are found; these may in part be due to departure of the lattice vibrations from the Debye spectrum. The thermal conductivity, in particular, is compared with the most recent theoretical work, and the predicted minimum at ~ 0.25Θ has not been found.