Admixtures to d-wave gap symmetry in untwinned YBa2Cu3O7 superconducting films measured by angle-resolved electron tunneling

Abstract

We report on an ab anisotropy of Jca¥b/Jcâ¥aâ‰1. 8 and IcRnâ¥b/IcRnâ ¥a≠1.2 in ramp-edge junctions between untwinned YBa2Cu3O7 and s-wave Nb. For these junctions, the angle Î with the YBa2Cu3O7 crystal b axis is varied as a single parameter. The RnA(Î) dependence presents twofold symmetry. The minima in IcRn at Π≠50° suggest a real s-wave subdominant component and negligible dxy-wave or imaginary s-wave admixtures. The IcRn(Î) dependence is well fitted by 83% dx2-y2-, 15% isotropic s-, and 2% anisotropic s-wave order parameter symmetry, consistent with Î"b/Î"a≠1.5. © 2005 The American Physical Society.