Comment on "Infrared signature of the superconducting gap symmetry in iron-arsenide superconductors", Y. M. Dai et al. arXiv:1106.4430

TL;DR

This paper critiques a recent optical study of a superconductor, highlighting contradictions with established experimental data and misapplications of theoretical models beyond their valid regimes.

Contribution

It provides a critical analysis pointing out flaws in the interpretation and theoretical application in the referenced superconductivity study.

Findings

Identifies contradictions with existing experimental data

Highlights misapplication of Mattis-Bardeen and BCS theories

Questions the validity of the original analysis

Abstract

Y. M. Dai et al. in their recent work arXiv:1106.4430 presented a reflectivity study of the in-plance optical conductivity of a $\textrm{Ba}_{0.6}\textrm{K}_{0.4}\textrm{Fe}_2\textrm{As}_2$ (BKFA) superconductor with $T_{\textrm{c}}\approx39K$. The single crystals used in this study are of high quality and the measurements are rather accurate. The authors analyzed the optical conductivity of BKFA in the framework of the Mattis-Bardeen theory and the BCS theory of superconductivity. This analysis, however, generates a series of severe contradictions with a large body of experimental data obtained with multiple probes as well as misuses both the Mattis-Bardeen and the BCS theories of superconductivity beyond their approximation regions.