Angular Position of Nodes in the Superconducting Gap of Quasi-2D Heavy-Fermion Superconductor CeCoIn5

The thermal conductivity of the heavy-fermion superconductor CeCoIn5 has been studied in a magnetic field rotating within the 2D planes. A clear fourfold symmetry of the thermal conductivity which is characteristic of a superconducting gap with nodes along the (±π,±π) directions is resolved. The thermal conductivity measurement also reveals a first-order transition at Hc2 , indicating a Pauli limited superconducting state. These results indicate that the symmetry most likely belongs to dx#sup 2#-y#sup 2# , implying that the anisotropic antiferromagnetic fluctuation is relevant to the superconductivity