Magnetic Tuning of the Metal-Insulator Transition for Uncompensated Arsenic-Doped Silicon

Barely insulating and barely metallic Si:As samples have been studied in the temperature range 4.2 K to 50 mK. Metallic samples show a new high-field magnetoresistance behavior explainable in terms of magnetic tuning of the critical density $N_c$. Insulating samples at fixed fields show Mott variable-range-hopping behavior and the increase of characteristic temperature $T_0\mathrm{}(N,H)\mathrm{}$ with $H$ results primarily from magnetic tuning of the localization-length exponent $\nu$. Magnetocapacitance results depend on field-induced changes in both $N_c$ and $\nu$.