The critical conductivity exponent of Si:P changes from near 1/2 in zero field to 0.86±0.15 in a magnetic field of 8 T, consistent with the theoretical expectation of 1. According to recent theory, similar behavior found earlier in Si:B, where spin-orbit scattering is strong, corresponds to the universality class for magnetic impurities. These measurements in Si:P thus constitute a clear determination of the critical conductivity exponent near the metal-insulator transition in the universality class for high magnetic field.

• Received 14 May 1993

DOI:https://doi.org/10.1103/PhysRevB.48.4941