Universal critical normal sheet resistance in ultrathin films

Abstract

A simple analysis is given to ultrathin-film systems. Based on the physical picture proposed that the superconducting-insulating phase transition at T-0 is a combined effect of the pairing and localization in two-dimensional systems, the normal-state sheet resistance is evaluated in the vicinity of the transition. It is found to be universal and equal to h/(2e${)}^2$, independent of the details of different samples as observed in experiments. A similar formulation can be also used to explain the quantized conductance in narrow channels.