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

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.