Comment on "Superconducting gap anisotropy vs. doping level in high-T_c cuprates" by C. Kendziora et al, PRL 77, 727 (1996)

TL;DR

This paper challenges prior conclusions that the superconducting gap in overdoped Bi-2212 is isotropic, proposing instead that it exhibits strong anisotropy with nodes, supported by new data and a refined theoretical model.

Contribution

The authors reinterpret existing Raman scattering data and present new measurements indicating a strongly anisotropic d_{x^{2}-y^{2}} gap with nodes in overdoped Bi-2212.

Findings

Data consistent with a d_{x^{2}-y^{2}} gap with nodes

Reinterpretation of Raman spectra supports anisotropic gap

Model includes spin fluctuations and impurity scattering

Abstract

In a recent paper Kendziora et al concluded that the superconducting gap in overdoped Bi-2212 is isotropic. From data obtained from electronic Raman scattering measurements, their conclusion was based on the observation that pair breaking peaks occured at approximately the same frequency in different scattering geometries and that the normalized scattering intensity at low energies was strongly depleted. We discuss a different interpretation of the raw data and present new data which is consistent with a strongly anisotropic gap with nodes. The spectra can be successfully described by a model for Raman scattering in a d_{x^{2}-y^{2}} superconductor with spin fluctuations and impurity scattering included.