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

Abstract

We report on an \textit{ab}-anisotropy of $J_{c\parallel b}/J_{c\parallel a}$ and $I_c{R}_{n\parallel b}/I_c{R}_{n\parallel a}\cong 1.2$ in ramp-edge junctions between untwinned YBa${}_2$Cu${}_3$O${}_7$ and $s$% -wave Nb. For these junctions, the angle $\theta$ with the YBa${}_2$Cu${}_3$O${}_7$ crystal b-axis is varied as a single parameter. The $R_n$A($\theta$)-dependence presents 2-fold symmetry. The minima in $I_c{R}_n$ at $\theta \cong 50^{\circ }$ 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 ${\Delta }_b/{\Delta }_a\cong 1.5$.

4 pages, 3 figures, to be published in Physical Review Letters

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