Low-temperature nodal-quasiparticle transport in lightly doped YBa2Cu3Oy near the edge of the superconducting doping regime -: art. no. 100502

In-plane transport properties of nonsuperconducting YBa2Cu3Oy (y=6.35) are measured using high-quality untwinned single crystals. We find that both the a- and b-axis resistivities show ln(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 YBa2Cu3Oy, as opposed to a recent report by Sutherland [Phys. Rev. Lett. 94, 147004 (2005)]. Besides, the present data demonstrate that the peculiar ln(1/T) resistivity divergence of cuprate is not a property associated with high magnetic fields.