Interlayer pair tunneling and gap anisotropy in YBa2Cu3O7-δ

Recent angle-resolved photoemission spectroscopy measurement observed a large $\mathrm{ab}$-axis gap anisotropy, $\ensuremath{\Delta}(0,\ensuremath{\pi})/\ensuremath{\Delta}(\ensuremath{\pi},0)=1.5,$ in clean ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}.$ This indicates that some subdominant component may exist in the ${d}_{{x}^{2}\ensuremath{-}{y}^{2}}$-wave dominant gap. We propose that the interlayer pairing tunneling contribution can be determined through an investigation of the order-parameter anisotropy. Their potentially observable features in transport and spin dynamics are also studied.