Comment on "Low-temperature phonon thermal conductivity of single-crystalline Nd_{2}CuO_{4}: Effects of sample size and surface roughness" by Li et al.

TL;DR

This paper critically examines previous experimental claims about phonon thermal conductivity in cuprates, arguing that the data do not support the presence of phonon specular reflection at low temperatures due to small phonon mean free paths.

Contribution

It provides a critical analysis showing that earlier experimental data do not support phonon specular reflection in high-T_c cuprates at low temperatures.

Findings

Phonon mean free path is much smaller than sample width above 100 mK.

Previous data do not support phonon specular reflection in cuprates.

Challenges prior interpretations of thermal conductivity data.

Abstract

In this Comment, we show that the experimental data reported by Li {\it et al.} (Phys. Rev. B {\bf 77}, 134501 (2008)) do not support the phonon specular reflection at low temperatures for high-T_c cuprates, because the phonon mean free path \ell calculated from their thermal conductivity data is much smaller than the averaged sample width above \sim 100 mK for both Nd_{2}CuO_{4} and YBa_{2}Cu_{3}O_{6.0} single crystals.