  Recent experiments show that an atomic step on the surface of atomically thin
metallic films can strongly affect electronic transport. Here we reveal
multiple and versatile effects that such a surface step can have on
superconductivity in ultrathin films. By solving the Bogoliubov-de Gennes
equations self-consistently in this regime, where quantum confinement dominates
the emergent physics, we show that the electronic structure is profoundly
modified on the two sides of the step, as is the spatial distribution of the
superconducting order parameter and its dependence on temperature and
electronic gating. Furthermore, the surface step changes non-trivially the
transport properties both in the proximity-induced superconducting order
parameter and the Josephson effect, depending on the step height. These results
offer a new route to tailor superconducting circuits and design atomically thin
hetero-junctions made of one same material.
