Phys. Rev. B 66, 064525 (2002)

Roberto Ocaña and Pablo Esquinazi

Abstract

We have measured the thermal conductivity tensor of a twinned YBa₂Cu₃O_7-x single crystal as a function of angle θ between the magnetic field applied parallel to the CuO₂ planes and the heat current direction, at different magnetic fields and at T=13.8 K. Clear fourfold and twofold variations in the field-angle dependence of κ_xx and κ_xy were, respectively, recorded in accordance with the d-wave pairing symmetry of the order parameter. The oscillation amplitude of the transverse thermal conductivity κ_xy⁰ was found to be larger than the longitudinal one, κ_xx⁰, in the range of magnetic field studied here (0 T<~B<~9 T). From our data we obtain quantities that are free from nonelectronic contributions, and they allow us a comparison of the experimental results with current models for the quasiparticle transport in the mixed state.