Determination of the symmetry of the superconducting pairing state and formation of a low-temperature normal metallic state in YBCO by electron irradiation

A key difference between a d-wave and an anisotropic s-wave superconductor is the expected effect of nonmagnetic point defects on T{sub c}. T{sub c} of the former becomes zero whereas T{sub c} of the latter attains a nonzero constant value beyond a critical concentration of impurities. We report the first observation that T{sub c} of an YBCO single crystal becomes zero after 4.1% of the planar oxygens O(2,3) are displaced by 400keV electron irradiation along the c-axis. Our data therefore indicate that YBCO is a d-wave superconductor. We also report evidence of a disorder-induced superconductor-to-normal-metal transition