Infrared Studies of the Onset of Conductivity in Ultra-Thin Pb Films

TL;DR

This study measures the infrared conductivity of ultra-thin Pb films, revealing behavior inconsistent with weak localization but aligning with two-dimensional percolation theory, due to their granular structure.

Contribution

First experimental infrared conductivity measurements of ultra-thin Pb films, highlighting inhomogeneous granular effects and supporting percolation theory models.

Findings

Infrared conductance increases with frequency in these films.

Disagreement with weak localization predictions.

Consistency with two-dimensional percolation theory.

Abstract

In this paper we report the first experimental measurement of the infrared conductivity of ultra-thin quenched-condensed Pb films. For dc sheet resistances such that $\omega \tau \ll 1$ the ac conductance increases with frequency but is in disagreement with the predictions of weak localization. We attribute this behavior to the effects of an inhomogeneous granular structure of these films, which is manifested at the very small probing scale of infrared measurements. Our data are consistent with predictions of two-dimensional percolation theory.