Thin film growth of layered cobalt-oxide Bi2Sr3Co2O9+δ nearly isomorphic to Bi2Sr2CaCu2O8+δ superconductors

Abstract

Thin films of Bi2Sr3Co2O9+δ, which is nearly isomorphic to Bi2Sr2CaCu2O8+δ, are grown in situ by molecular beam epitaxy with pure ozone. For producing a molecular beam of Co by a Knudsen cell, we used MgO as a crucible material. The c-axis oriented films are successfully grown on Nd:YAlO3 (001) substrates, which are untwinned with their structural modulation along Nd:YAlO3[100]. With cooling the films from room temperature, it was found that they show a metallic behavior first (dρ/dT≳0), and then a semiconducting one at lower temperatures (dρ/dT<0). One of the films, which shows the lowest resistivity, exhibits dρ/dT≳0 down to 86 K.