Spin dynamics of nearly localized electrons.

We have measured the electron spin resonance signal of metallic Si:P near the metal-insulator transition down to a temperature of 30 mK. The paramagnetic spin susceptibility and the resonance linewidth are found to increase with falling temperatures. The effective interaction of the electron spin with the phosphorus nuclei is argued to be enhanced with the slowing down of spin diffusion leading to an increase in linewidth. These results are compared with recent theories for the susceptibility and linewidth of disordered interacting electron systems.