Evidence of order-parameter symmetry and of a normal metallic state in electron-irradiated YBa2Cu3O7-8 (YBCO)

Abstract

A key difference between a d-wave superconductor and an anisotropic s-wave one is the expected effect of nonmagnetic point defects on Tc. For the former, Tc becomes zero, whereas for the latter, Tc reaches a nonzero constant value beyond a critical concentration of impurities. We report that Tc of single-crystal YBCO becomes less than 12K, our lowest temperature, when 4.1% of the planar oxygens 0(2,3) are displaced by 400keV electrons, incident along the e-axis. Our data therefore suggest that YBCO is a d-wave superconductor. We also report a disorder-induced transition from superconductor-to-normal metal.