Persistence of an Energy Scale in Over-Doped High-Tc Superconductors

TL;DR

This paper challenges previous claims that sharp modes are unimportant for superconductivity in over-doped cuprates, arguing that earlier conclusions were based on insensitive measurements and misinterpreted data.

Contribution

The authors demonstrate that previous experimental conclusions about the disappearance of sharp modes in over-doped cuprates are unfounded due to measurement insensitivity and data misinterpretation.

Findings

Optics experiments are insensitive to anisotropic cuprate properties.

Existing ARPES data was misrepresented in prior studies.

The claimed disappearance of sharp modes is not supported by accurate analysis.

Abstract

Citing the disappearance of a sharp peak in the electron self-energy, extracted from optics and angle-resolved photoemission spectroscopy (ARPES) experiments in deeply over-doped copper-oxide superconductors with Tc of 55-60K, Hwang, Timusk et al. argue that sharp modes, be they phononic or magnetic in origin, are not important for superconductivity in the cuprates. If true, this would have been an important progress. We show, however, their conclusions are unfounded because of the insensitivity of the optics experiment in studying strongly anisotropic material like the cuprates, and a misrepresentation of existing ARPES data. In an added note, we refute the claim by Valla, Timusk et. al. that the doping level of the data presented in the first part of this comment is lower than reported.