Conductivity maximum at low temperatures in metallic Si:P near the metal-insulator transition

High-resolution measurements of the electrical conductivity σ( T ) below T = 1 K of uncompensated Si:P with P concentration N above the critical concentration N c are reported. In a narrow N range, roughly 10% above N c , σ( T ) actually exhibits a shallow maximum which rapidly shifts to higher T with decreasing N . These features, as well as the strong shift of the maxima towards higher T with magnetic field, are interpreted in terms of the suppression of the triplet particle-hole channel in the electron-electron interaction, arising from spin-flip scattering due to local magnetic moments.