The low-temperature specific heat and electrical conductivity have been measured on samples of Si: P with well-characterized electron densities. The metallic conductivity in the limit of zero temperature is found to vary considerably more rapidly than the electronic density of states for donor densities near the metal-insulator transition. Mott's analysis of the Kubo-Greenwood formulation provides an adequate description of the results only at higher densities than expected.

• Received 10 August 1981

DOI:https://doi.org/10.1103/PhysRevB.24.4886