Electronic transport in ultrathin epitaxial Pb films on Si(111) surfaces

Abstract

Epitaxial metallic films are candidates for two-dimensional (2D) electronic systems. In that respect, the DC conductivity is a good tool to check the electronic structure for quantum phenomena. The annealed Pb films on the Si(111) 7×7 and on the Si(111) 3 × 3 Pb surfaces show a very contrary behavior to that of classical metals. Whereas at 8 K and a coverage above 6 monolayers (ML) the conductivity is well described by the classical Drude model with the mean free path in the order of the film thickness, at low coverages, a metal–insulator transition (MIT) is observed. The conductivity shows different regimes pointing to strong localization, weak localization or classical behavior depending on film thickness, annealing and measuring temperature. Structural changes modify directly the conductivity. Superconductivity with the critical temperature close to the bulk value is observed in annealed films with a thicknesses down to 4 ML. Resistivity oscillations during the growth of the film on Si(111)- 3 × 3 Pb with 1 ML and 2 ML period are reported.