METAL-INSULATOR-TRANSITION IN SI-X (X=P,B) - ANOMALOUS RESPONSE TO A MAGNETIC-FIELD

The zero-temperature magnetoconductivity of just-metallic Si:P scales with magnetic field H and dopant concentration n lying on a single uni versal curve: sigma(n,H)/sigma(n,0)= G[H(-delta)Delta n] with a magnet ic-field crossover exponent delta approximate to 2. We note that Si:P, Si:B, and Si:As all have unusually large crossover exponents near 2, and suggest that this anomalously weak response to a magnetic field, D elta n(c)proportional to H-delta is a common feature of uncompensated doped semiconductors.