Comparison of the superconducting pairing between the oxide superconductorsBa1−xKxBiO3andYBa2Cu3O6.6using phase-sensitive Josephson tunneling

We compare the Josephson tunneling of a suspected d-wave superconductor, ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6.6}$, with that of another oxide superconductor ${\mathrm{Ba}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{K}}_{\mathrm{x}}$ ${\mathrm{BiO}}_3$. For comparison the critical current ${\mathrm{I}}_{\mathrm{c}}$ vs applied field of a single-crystal Josephson junction injecting supercurrent in the [110] direction is measured for both superconductors. For the ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6.6}$ single crystal ( ${\mathrm{T}}_{\mathrm{c}}$=60 K), the critical current is a minimum at zero applied field, while for ${\mathrm{Ba}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{K}}_{\mathrm{x}}$ ${\mathrm{BiO}}_3$, the critical current reveals a maximum at zero field. The results are consistent with a d-wave order parameter for ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{6.6}$, and conventional s-wave superconductivity for ${\mathrm{Ba}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{K}}_{\mathrm{x}}$ ${\mathrm{BiO}}_3$.