We report on an $ab$ anisotropy of $J_{c\parallel b}/J_{c\parallel a}\cong 1.8$ and $I_c{R}_{n\parallel b}/I_c{R}_{n\parallel a}\cong 1.2$ in ramp-edge junctions between untwinned ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ and $s$-wave Nb. For these junctions, the angle $\theta$ with the ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7$ crystal $b$ axis is varied as a single parameter. The $R_{n}A(\theta )$ dependence presents twofold symmetry. The minima in $I_c{R}_n$ at $\theta \cong 50°$ suggest a real $s$-wave subdominant component and negligible $d_{xy}$-wave or imaginary $s$-wave admixtures. The $I_c{R}_n(\theta )$ dependence is well fitted by 83% $d_{x^2-y^2}$-, 15% isotropic $s$-, and 2% anisotropic $s$-wave order parameter symmetry, consistent with ${\Delta }_b/{\Delta }_a\cong 1.5$.

• Received 15 April 2005

DOI:https://doi.org/10.1103/PhysRevLett.95.257001