Interlayer pair tunneling and gap anisotropy in YBa₂Cu₃O_7-δ

Recent angle-resolved photoemission spectroscopy measurement observed a large ab-axis gap anisotropy, Δ(0,π)/Δ(π,0) = 1.5, in clean YBa₂Cu₃O_7-δ. This indicates that some subdominant component may exist in the d_x2-y2-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.