ESR studies of compensated Si:P,B near the metal-insulator transition

We have studied the ESR properties of three compensated n-type Si:P,B samples ner the metal-insulator transition covering the low-temperature regime from 30 mK to 10 K. We find that both the susceptibility and the ESR linewidth increase dramatically as the temperature is lowered, and in the metallic Si:P,B samples the susceptibility increase is more than in similar uncompensated Si:P samples. We compare results for the insulating phase with numerical calculations, then discuss the metallic region in light of various theoretical models for the low-temperature thermodynamic behavior.