Metallic impurity conduction and metal-nonmetal transition in n-InSb at low temperature

The resistivities of n-InSb in the metallic impurity conduction range were investigated down to 20 mK at zero and 100 Oe of applied magnetic field. Samples in the metallic impurity conduction range were divided into two groups. The resistivities of samples with high carrier concentration take maximum values at several hundreds mK. Below this temperature, the resistivities decrease when the temperature is lowered. On the other hand, the resistivities of samples with low carrier concentration increase when the temperature is lowered. We found that the dominant mechanisms which determine the sign of the temperature coefficient of the resistivities at zero magnetic field are different from each other in the two groups of the samples.