Evidence of a T=0 Quantum Critical Point Associated with the Crossover from Weak to Strong Localization

Abstract

A crossover between logarithmic and exponential temperature dependence of the conductance (weak and strong localization) has been observed in ultrathin films of metals deposited onto substrates held at liquid helium temperatures. The resistance at the crossover is well defined by the onset of a nearly linear dependence of conductance on thickness at fixed temperature in a sequence of in situ evaporated films. The results of a finite size scaling analysis treating thickness as a control parameter suggest the existence of a T=0 quantum critical point which we suggest is a charge, or electron glass melting transition.