Influence of temperature on the nodal properties of the longitudinal thermal conductivity of YBa<InlineEquation ID="Equ1"> <EquationSource Format="TEX">$\mathsf{_2}$</EquationSource> </InlineEquation>Cu<InlineEquation ID="Equ2"> <EquationSource Format="TEX">$\mathsf{_3}$</EquationSource> </InlineEquation>O<InlineEquation ID="Equ3"> <EquationSource Format="TEX">$\mathsf{_{7-x}}$</EquationSource> ...

The angle dependence at different temperatures of the longitudinal thermal conductivity <InlineEquation ID="Equ4"> <EquationSource Format="TEX">$\kappa_{xx}(\theta)$</EquationSource> </InlineEquation> in the presence of a planar magnetic field is presented. In order to study the influence of the gap symmetry on the thermal transport, angular scans were measured up to a few Kelvin below the critical temperature T<Subscript>c</Subscript>. We found that the four-fold oscillation of <InlineEquation ID="Equ5"> <EquationSource Format="TEX">$\kappa_{xx}(\theta)$</EquationSource> </InlineEquation> vanishes at T > 20K and transforms into a one-fold oscillation with maximum conductivity for a field of 8 T applied parallel to the heat current. Nevertheless, the results indicate that the d-wave pairing symmetry remains the main pairing symmetry of the order parameter up to T<Subscript>c</Subscript>. Numerical results of the thermal conductivity using an Andreev reflection model for the scattering of quasiparticles by supercurrents under the assumption of d-wave symmetry provide a semiquantitative description of the overall results. Copyright Springer-Verlag Berlin/Heidelberg 2003