Thermal conductivity of unconventional superconductors in the vortex state.

Generalizing a theory of Houghton and Maki for clean type-II superconductors to the case of unconventional superconductors, we study systematically the anisotropy in the thermal conductivity in the vortex state in the immediate vicinity of [ital B]=[ital H][sub [ital c]2]([ital T]) the upper critical field. The result is compared with recent experimental data on [ital K][sub [ital j]][sup [ital i]] in a single crystal of UPt[sub 3], where [ital i] and [ital j] are the directions of the magnetic field and the heat current. Among superconducting wave functions (i.e., [ital l][le]3 and belonging to [ital D][sub 6] symmetry), polar ([ital A][sub 1[ital u]]) and hybrid ([ital E][sub 1[ital g]]) terms describe consistently the anisotropy between [ital K][sub [ital b]][sup [ital b]] and [ital K][sub [ital b]][sup [ital a]]. However, none of them appears to describe the anisotropy between [ital K][sub [ital b]][sup [ital c]] and [ital K][sub [ital b]][sup [ital a]].