Surface conductivity properties of high-T_C superconductors

High quality c-axis oriented YBCO thin films have been prepared by dc magnetron sputtering from a stoichiometric ceramic target on single crystalline LaAlO₃ substrates. Ba-122 thin films have been fabricated by pulsed laser deposition (PLD) on MgO single crystalline substrates with Fe buffer layer. surface conductivity properties of high-Tc superconductors have been investigated by SPM methods. Spiral pyramidal objects created during growth process have been revealed by Scanning Spreading Resistance Microscopy (SSRM) on Ba-122 films deposited by PLD. It has been shown that surface conductivity is highly inhomogeneous and should be taken into account when micro-scale planar junctions are measured. Moreover, it can be limiting factor for nano-scale applications. We propose that such inhomogeneous surface conductivity is due to degraded insulating surface layer of varying thickness and inhomogeneous distribution of oxygen near the surface. Gradual decrease of YBCO average surface conductivity in both air and pure nitrogen atmosphere due to out-diffusion of oxygen has been observed by SSRM. (authors)