Admixtures to d-wave gap symmetry in untwinned YBa2Cu3O7 superconducting films measured by angle-resolved electron tunneling -: art. no. 257001

We report on an ab anisotropy of J(c parallel to b)/J(c parallel to a)congruent to 1.8 and IcRn parallel to b/I(c)R(n parallel to a)congruent to 1.2 in ramp-edge junctions between untwinned YBa2Cu3O7 and s-wave Nb. For these junctions, the angle theta with the YBa2Cu3O7 crystal b axis is varied as a single parameter. The R(n)A(theta) dependence presents twofold symmetry. The minima in IcRn at theta congruent to 50 degrees suggest a real s-wave subdominant component and negligible d(xy)-wave or imaginary s-wave admixtures. The IcRn(theta) dependence is well fitted by 83% d(x)(2)-y(2)-, 15% isotropic s-, and 2% anisotropic s-wave order parameter symmetry, consistent with Delta(b)/Delta(a)congruent to 1.5.