Tuning correlation and localization lengths with high magnetic fields near the metal-insulator transition

Various experiments at low-temperatures on Si:As in the critical regime (0·8 < N/N c< 1·2) near the metal-insulator transition have yielded information on magnetic-field-induced changes in the correlation and localization lengths. The measurements include magnetoresistance of metallic samples, magnetocapacitance, a.c. magnetoconductance, and the field dependence of Mott variable-range-hopping conduction for insulating samples. The field-induced changes in ζ(N, H) are interpreted in terms of field-induced changes in the critical density Nc and the correlation-localization-length exponent v(H). The implications of the results for the Shapiro phase diagram are discussed.