Effect of a magnetic field on the critical conductivity exponent at the metal-insulator transition.

Abstract

From measurements of the resistivity down to 70 mK in magnetic fields to 7.5 T of a series of just-metallic, uncompensated, p-type Si:B samples, we have established that the critical exponent which characterizes the approach of the zero-temperature conductivity to the insulating phase changes from \ensuremath{\nu}=0.${65}_{\mathrm{\ensuremath{-}}0.14}^{+0.05}$ in zero field to \ensuremath{\nu}=1.${0}_{\mathrm{\ensuremath{-}}0.20}^{+0.10}$ in a magnetic field of 7.5 T. This is the first clear experimental evidence for a change in universality class at the metal-insulator transition caused by the application of a magnetic field.