crystals in precisely oriented vector magnetic fields*

Temperature and magnetic field dependent thermal conductivity, κ(T,H), was measured in high quality single crystals of KFe₂As₂ in precisely oriented magnetic fields in 2D vector magnet for current along the tetragonal b-direction. For fields along a- and c-tetragonal axes we observed monotonic quasi-linear increase of κ(H) followed by a rapid step-wise increase towards the upper critical field, H_c2, consistent with expectations for clean nodal superconductors. Anomalous, increase of κ(T)/T on cooling is found in H∥a configuration for magnetic fields just below H_c2=5 T. These observations are contrasted with the previous heat capacity measurements.