Superconducting gap structure of antiferromagnetic heavy-fermion superconductor UPd2Al3 studied by thermal conductivity measurements with rotating magnetic field

Heavy fermion superconductor UPd2Al3 exhibits intriguing behavior that superconductivity coexists with antiferromagnetic ordering in atomic scale. We investigated the superconducting gap structure of UPd2Al3 by thermal conductivity measurements with rotating magnetic field H in various directions relative to the crystal axes. Distinct two-fold oscillation of thermal conductivity was observed with rotating H within the ac plane, while no oscillation was observed within the basal plane. These angular variations indicate the superconducting gap function Δ(k) has a single line node orthogonal to the c-axis. Our experimental results deduce the superconducting gap function of UPd2Al3 as d-wave symmetry with a form Δ(k) = Δ0cos(kzc).