Structure and properties of a class of CeO2-based biepitaxial YBa2Cu3O7-delta Josephson junctions

An innovative biepitaxial technique for the fabrication of YBa2Cu3O7-delta artificial grain-boundary Josephson junctions is proposed. The structure was specifically designed to analyze the effects of anisotropy, both in the order parameter and in the crystallographic structure of YBa2Cu3O7-delta, on the Josephson current crossing the artificial grain boundary. Samples are grown on vicinal (110) oriented SrTiO3 substrates, and a CeO2 film is employed as a seed layer. Crystallography and morphology of the samples are analyzed, thus allowing us to infer the nature of the grain boundary. Our measurements show that the obtained grain boundary, besides possessing a unique and complex structure, exhibits very peculiar Josephson and tunnel-like properties. The intrinsic flexibility of the biepitaxial technique is employed to modify the in-plane angle of the grain-boundary interface, allowing for the realization of symmetrical, asymmetrical, and intermediate configurations on the same substrate. Accordingly, junctions exhibiting different kinds of magnetic field dependence of the Josephson current are obtained on the same chip. Evidence of d-wave-induced effects and of a dielectric character of the barrier is obtained by the transport measurements.