The smallest length scale near the metal-insulator transition

It is shown that very near the metal-insulator transition in a three-dimensional system at very low temperatures (T), the inelastic diffusion length (Li) is reduced and may become the smallest length scale. In this region the conductivity, sigma, follows the law sigma = sigma 0+mT^1/2where the T^1/2dependence arises primarily from a diffusion length Li approximately sigma 0³2//T^1/2which is smaller than the interaction length LT approximately sigma ¹2//T^1/2when sigma 0 is small. The authors present experimental evidence for these results. In particular, for InSb they find m varies as sigma 0^-3/2and for compensated GaAs they find negative magnetoresistance near the transition, which yields Li approximately T^-1/2.