Interplay between the atomic structures and superconductivity of two-monolayer Pb films

Superconductors with reduced dimensionality have been widely explored for their exotic superconducting behaviors. Especially, at the two-dimensional limit, two-monolayer Pb films with two types of structures provide an ideal platform to unveil the underlying superconducting mechanism [ Science 324 , 1314 (2009)]. Here, by combining scanning tunneling microscopy (STM) with the first-principle calculations, we successfully identify that these two types have different atomic lattice structures with varying stacking phases, which further enables us to calculate the phonon spectrum and electron phonon coupling strength of each type. The theoretical calculations are in good agreement with tunneling spectroscopy measurements of the superconducting transition temperatures ( T c ), which established a correlation between atomic structures and superconductivity. Moreover, it was observed that the higher T c of these two types also possess higher out-of-plane upper critical magnetic fields ( H c2 ). These findings will provide important new insights into two-dimensional superconductivity at the atomic level.