  Extended defects are known to strongly affect nanoscale superconductors. Here
we report the properties of superconducting nanoribbons with a constriction
formed between two adjacent step-edges, by solving the Bogoliubov-de Gennes
equations self-consistently in the regime where quantum confinement is
important. Since the quantum resonances of the superconducting gap in the
constricted area are different from the rest of the nanoribbon, such
constriction forms a quantum-confined S-S'-S Josephson junction, with a broadly
tunable performance depending on the length and width of the constriction with
respect to the nanoribbon, and possible gating. These findings provide an
intriguing approach to further tailor superconducting quantum devices where
Josephson effect is of use.
