Comment on "Onset of Boson Mode at the Superconducting Critical Point of Underdoped YBa2Cu3Oy"

TL;DR

This paper critically evaluates claims of a novel bosonic mode and charge-neutral fermions in underdoped YBa2Cu3Oy, arguing that the evidence presented is unconvincing and disputing their existence.

Contribution

It provides a critical analysis challenging the interpretation of thermal conductivity data as evidence for new bosonic modes and charge-neutral fermions.

Findings

The claims of a bosonic mode are not supported by the data.

The evidence for charge-neutral fermions is questionable.

The original interpretation may be flawed or incomplete.

Abstract

In a recent Letter [Phys. Rev. Lett. 97, 207001 (2006)], Doiron-Leyraud et al. reported a study of low-temperature thermal conductivity of underdoped YBa2Cu3Oy across the superconductor-insulator boundary and argued for a novel bosonic mode as well as charge-neutral fermions. In this Comment, we show that both of these claims are dubious.