Low-temperature nodal-quasiparticle transport in lightly doped YBa_{2}Cu_{3}O_{y} near the edge of the superconducting doping regime

TL;DR

This study investigates the low-temperature transport properties of lightly doped nonsuperconducting YBa2Cu3Oy, revealing localization of nodal quasiparticles and challenging previous claims of a thermal metal state.

Contribution

It provides new experimental evidence showing the absence of a thermal metal phase in lightly doped YBa2Cu3Oy and clarifies the nature of resistivity divergence at low temperatures.

Findings

Resistivities show log(1/T) divergence down to 80 mK.

Nodal quasiparticles become localized at low temperatures.

No evidence of a thermal metal phase in nonsuperconducting YBa2Cu3Oy.

Abstract

In-plane transport properties of nonsuperconducting YBa_{2}Cu_{3}O_{y} (y = 6.35) are measured using high-quality untwinned single crystals. We find that both the a- and b-axis resistivities show log(1/T) divergence down to 80 mK, and accordingly the thermal conductivity data indicate that the nodal quasiparticles are progressively localized with lowering temperature. Hence, both the charge and heat transport data do not support the existence of a "thermal metal" in nonsuperconducting YBa_{2}Cu_{3}O_{y}, as opposed to a recent report by Sutherland {\it et al.} [Phys. Rev. Lett. {\bf 94}, 147004 (2005)]. Besides, the present data demonstrate that the peculiar log(1/T) resistivity divergence of cuprate is {\it not} a property associated with high-magnetic fields.