Thermal conductivity tensor inYBa2Cu3O7−x: Effects of a planar magnetic field

Abstract

We have measured the thermal conductivity tensor of a twinned ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}x}$ single crystal as a function of angle $\ensuremath{\theta}$ between the magnetic field applied parallel to the ${\mathrm{CuO}}_{2}$ planes and the heat current direction, at different magnetic fields and at $T=13.8 \mathrm{K}.$ Clear fourfold and twofold variations in the field-angle dependence of ${\ensuremath{\kappa}}_{\mathrm{xx}}$ and ${\ensuremath{\kappa}}_{\mathrm{xy}}$ were, respectively, recorded in accordance with the d-wave pairing symmetry of the order parameter. The oscillation amplitude of the transverse thermal conductivity ${\ensuremath{\kappa}}_{\mathrm{xy}}^{0}$ was found to be larger than the longitudinal one, ${\ensuremath{\kappa}}_{\mathrm{xx}}^{0},$ in the range of magnetic field studied here $(0 \mathrm{T}<~B<~9 \mathrm{T}).$ 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.