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

TL;DR

This study investigates the anisotropic superconducting gap symmetry in untwinned YBa2Cu3O7 films using angle-resolved electron tunneling, revealing a dominant d-wave component with a subdominant s-wave admixture.

Contribution

The paper provides experimental evidence for admixtures to the d-wave gap symmetry in YBa2Cu3O7, quantified through angle-resolved tunneling measurements.

Findings

Observed anisotropy in critical current and resistance ratios.

Detected minima in I_c R_n at specific angles indicating s-wave admixture.

Quantified the gap symmetry as 83% d-wave, 15% isotropic s-wave, and 2% anisotropic s-wave.

Abstract

We report on an \textit{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 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 $\Delta_{b}/\Delta_{a} \cong 1.5$.