The Demise of Superfluid Density in Overdoped La2−x Sr x CuO4 Films Grown by Molecular Beam Epitaxy

Abstract

We have synthesized La2−xSrxCuO4 thin films using atomic layer-by-layer molecular beam epitaxy (ALL-MBE). The films are high-quality—singe crystal, atomically smooth, and very homogeneous. The critical temperature (Tc) shows a very little (<1 K) variation within a film of 10×10 mm 2 area. The large statistics (over 2000 films) is crucial to discern intrinsic properties. In these films, we have measured the absolute value of the magnetic penetration depth λ with the accuracy better than 1 % and mapped densely the entire overdoped side of the La2−xSrxCuO4 phase diagram. A new scaling law is established accurately for the dependence of Tc on the superfluid density. The scaling we observe is incompatible with the standard Bardeen-Cooper-Schrieffer picture and points to local pairing.