The scaling theory and the minimum metallic conductivity

The scaling theory of conduction in non-crystalline solids is examined, particularly with regard to its conclusion that the conductivity of a metal tends continuously to zero at a mobility edge. Limiting ourselves to the theory of non- interacting electrons, we present certain arguments against this result. A new suggestion which we introduce is that the value (gc) for which the scaling function β(g) vanishes does not correspond to the mobility edge at which Anderson localization sets in, but to a new phenomenon which may be observed in certain cases. A possible weakness in the scaling theory is pointed out.