Comment on "Orbital Order, Structural Transition and Superconductivity in Iron Pnictides" [arXiv:1010.0129] by Yanagi et al

TL;DR

This paper critiques Yanagi et al.'s claim that orbital fluctuations from orthorhombic phonons explain high-temperature superconductivity in iron pnictides, arguing their phonon model is inconsistent and insufficient.

Contribution

It clarifies the inconsistency in Yanagi et al.'s phonon treatment and challenges the proposed mechanism for superconductivity in iron pnictides.

Findings

Orthorhombic phonon is acoustic, not optical.

Orbital fluctuations at q~0 cannot explain high-Tc superconductivity.

Inconsistent treatment of phonon energy in Yanagi et al.'s work.

Abstract

In contrast to the claim by Yanagi et al. in Ref. [1], the development of orbital fluctuations at $q ~ 0$ due to the "orthorhombic phonon" is unable to explain the high-Tc superconductivity in iron pnictides. The reason is that the orthorhombic-phonon is acoustic with the energy $\omega_q \propto q$, although the authors in Ref. [1] treated it as optical phonon ($\omega_o=0.02 eV$) inconsistently.