Anisotropy of upper critical field and surface superconducting state in the intermediate-valence superconductor CeIr3

CeIr3 is a Ce-based superconductor with a superconducting transition temperature Tc=3.4 K in an intermediate-valence state. We grew high-quality single crystals of CeIr3 using the Czochralski method, and measured the electrical resistivity, magnetic torque, and specific heat. The anisotropy of the superconducting upper critical field Hc2 was determined. The temperature dependence of Hc2, obtained from the resistivity measurements, suggests the multiband character of the superconductivity in CeIr3. Different field-angle dependencies of Hc2 in electrical transport and thermodynamic measurements indicate the robust surface effect in the bulk superconductivity of CeIr3. We analyzed the surface superconductivity based on simple models to reveal the bulk superconducting properties. Our results support the isotropic bulk superconducting state and robust surface superconductivity in CeIr3 single crystals.