The Morphology And Interfacial Effects On The R-T Curve Of Two Unit-Cell Thick Ultrathin Yba2cu3o7-Delta Film

Two unit-cell thick ultrathin YBa2Cu3O7-delta films were grown on (100) SrTiO3 substrates with a 400 Angstrom thick PrBa2Cu3O7-delta buffer layer by DC magnetron sputtering. The morphology was observed by both scanning electron microscopy and atomic force microscopy. An island-like growth mode was found; the heights of the islands differ mostly from each other by the YBCO c-axis length or half of the c-axis length. The zero-resistance temperature T-co of the film is 35 K, with a transition width of about 40 K. The R-T curve in the superconducting transition state can be analyzed by the Kosterlitz-Thouless transition and fluctuation-enhanced conductivity, and in the normal state can be described by the effects of interface (surface) and buffer layer conductance.