CRITICAL CONDUCTIVITY EXPONENT FOR SI-B

We have determined the critical exponent which characterizes the approach of the zero-temperature conductivity to the insulating phase from measurements down to 60 mK of the resistivity of a series of just-metallic uncompensated p-type Si:B samples with dopant concentrations near the critical concentration for the metal-insulator transition. Our results indicate a critical exponent for Si:B of 0.65(-0.14)+0.05, which is close to the "anomalous" values near 1/2 found for the uncompensated n-type silicon-based semiconductors Si:P, Si:As, and Si:Sb. This implies that, despite strong spin-orbit scattering, Si:B belongs to the same universality class as other silicon-based systems.