Thermal conductivity of superconducting UPt₃ versus magnetic field: probing the gap structure

The thermal conductivity (κ) of the heavy-fermion superconductor UPt₃ has been measured as a function of magnetic field (H) on a single crystal with the heat current in the basal plane. At low fields, where the scattering of heat carriers by vortices is thought to be important, κ(H) depends on the relative orientation of field and current. On the other hand, in the vicinity of the upper critical field, the dependence of κ(H) on the orientation of the field throws new light on the structure of the superconducting gap.