CRITICAL-BEHAVIOR OF THE CONDUCTIVITY IN METALLIC N-TYPE INP CLOSE TO THE METAL-INSULATOR-TRANSITION

The metal-insulator transition (MIT) induced by a magnetic field, in barely metallic and compensated n-type InP has been re-examined. Using new analysis methods, we have determined the magnetic field for which the conductivity change from a metallic behaviour to a variable-range hopping regime. On the metallic side of the MIT, the electrical conductivity is found to obey sigma = sigma-0 + mT(s) down to 60 mK; the zero-temperature conductivity can be described by a scaling law with an exponent nu = 1 and there is no evidence for a minimum metallic conductivity. As the MIT is approached, we observe a clear crossover from a T1/2 to T1/3 temperature dependence of the conductivity, which is related to a competition between two length scales: the correlation length and the interaction length.