Spin dynamics across the metal-insulator transition.

A theoretical study of the dynamics of electron spins in disordered insulators and metals is performed. Spin diffusion is found to slow down at low temperatures, making the system unusually sensitive to spin-dependent perturbations. This sensitive shows up in an unusual frequency and temperature dependence of the linewidth and resonance frequency of the electron spin resonance (ESR) signal. These results are used to interpret recent ESR measurements in phosphorus doped silicon in both the insulating and metallic phases, and good agreement is obtained with experiment.