Comment on Evolution of the electronic excitation spectrum with strongly diminishing hole density in superconducting Bi-2212 (J. W. Alldredge et al., Nature Phys. 4, 319 (2008))

TL;DR

This paper critiques a study on the evolution of the electronic excitation spectrum in Bi-2212 superconductors, highlighting issues with their fitting method and interpretation of the energy scale Delta_0(p).

Contribution

The paper provides a critical analysis of the fitting procedure and conclusions drawn in the referenced STM study on Bi-2212 doping levels.

Findings

The fitting method using G = aE is questioned for its validity.

The interpretation of the energy scale Delta_0(p) is challenged.

The paper suggests the original conclusions may be misleading.

Abstract

In a recent article, Alldredge et al. reported tunnelling data obtained at T = 4.2 K by STM in Bi-2212 having different doping levels, p, and a new way to fit the measured differential conductances, g(V), which are linearly proportional to the local density of states of quasiparticle excitations at the surface, N(E). The main point of the fitting procedure is to use an energy-dependent inelastic scattering rate, G = aE (a is a constant). They argue that by using an equation of the d-wave BCS density of states (Bardeen-Cooper-Schrieffer) modified by Dynes et al. with G = aE, they were able to fit any conductance obtained in Bi-2212 with a doping level between 0.1 and 0.22. In addition, they discuss a new energy scale Delta_0(p) similar to that obtained in Raman measurements. Unfortunately, the paper is misleading.