Insensitivity of atomic point contact conductance to a moiré structure

To elucidate the mechanism of electron transport through atomic point contacts, we investigated the contact-site dependence of electrical conductance on the periodical structure of a moire pattern observed on a Pb overlayer by scanning tunneling microscopy (STM). In order to eliminate the influence of atomic-site dependence on the conductance, we measured the point contact conductance on sites equivalent in an atomic surface lattice but different in the moire periodical structure, and found that the conductance does not depend on the contrast of the moire pattern. The moire-insensitive conductance indicates a dominant role of local atomic geometry in the point contact conductance. We also revealed that apparent barrier height in the tunneling regime is dependent on the contrast of the moire pattern, and that the moire contrast observed by STM on a 7-monolayer thin film originates from the barrier height difference at small bias voltages.