Smooth surfaces in very thin GdBa2Cu3O7−δ films for application in superconducting tunnel junctions

This paper provides a systematic analysis of the morphology and the superconducting critical temperature obtained in very thin GdBa2Cu3O7−δ films grown on (0 0 1) SrTiO3 substrates by DC sputtering. We find that the use of a very thin SrTiO3 buffer layer (≈2 nm) modify the nucleation of GdBa2Cu3O7−δ on the surface of the substrate reducing the formation of 3 dimensional clusters. Our results demonstrate that 16 nm thick GdBa2Cu3O7−δ films with an average root-mean-square (RMS) smaller than 1 nm and large surface areas (up 10 μm2) free of 3 dimensional topological defects can be obtained. In films thinner than 24 nm the onset (zero resistance) of superconducting transition of the films is reduced, being close to liquid nitrogen. This fact can be associated with stress reducing the orthorhombicity and slightly drop in oxygen stoichiometry.