Quasiparticle thermal conductivity in the vortex state of high-T-c cuprate

We present the results of a microscopic calculation of the longitudinal the rmal conductivity, kappa(xx), of a d-wave superconductor in the mixed stale . Our results show an increase in the thermal conductivity with the applied field at low temperatures and a decrease followed by a nearly held indepen dent kappa(xx)(H) at higher temperatures, in qualitative cement with the ex perimental results. We discuss the relationship between the slope of the su perconducting gap and the plateau in kappa(xx)(H).