Comment on `Anomalously Large Gap Anisotropy in the a-b Plane of Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\delta }$'

Abstract

Comment on `Anomalously Large Gap Anisotropy in the a-b Plane of Bi${}_2$Sr${}_2$CaCu${}_2$O${}_{8+\delta }$', Kazumasa Miyake and Osamu Narikiyo, In a recent Letter, Shen and collaborators [Phys. Rev. Lett. {\bf 70}, 1555 (1993)] reported that angle-resolved photoemission spectra (ARPES) in Bi-2212 cuprate superconductor far below $T_{\mathrm{c}}$ has anomalously large anisotropy and then concluded that the symmetry of Cooper pair is likely to be $d_{x^2-y^2}$, i.e., ${\Delta }_{\mathbf{k}}=\Delta (\cos k_{x}a-\cos k_{y}a)$. In this Comment we point out that the interpretation done by Shen {\it et al\/.}, where the shift of edge near Fermi level has been identified with the gap ${\Delta }_{\mathbf{k}}$, is not unambiguous, and that a possibility of $d_{xy}$ pairing, i.e., ${\Delta }_{\mathbf{k}}=2\Delta \sin k_{x}a\sin k_{y}a$, cannot be ruled out.

5 pages, Submitted to the Comment section of Phys. Rev. Lett