Abstract
Pb and Ga are immiscible in bulk form. Here, we show that atomically-smooth Pb_(1-x)Ga_x (x ~0.06) alloy films can be stabilized on a Si(111)-7x7 substrate by quantum confinement. Similar to the case of pure Pb, the alloy films follow a bilayer-by-bilayer growth mode but the resulting quantum growth morphology is remarkably different. Their superconducting transition temperatures indicate hole doping, supporting the notion that Ga atoms are substitutionally incorporated. The critical current densities are very high and exhibit a unique non-monotonic temperature dependence. This critical current anomaly is a direct consequence of the exceptional film morphology and is attributed to a superconducting transition inside two-monolayer thick vortex pinning centers.
