Superconducting and Fermi Surface Properties of a Valence Fluctuation Compound CeIr2

CeIr2 was reported as a valence fluctuation compound with a superconducting transition temperature of similar to 0.3 K. To investigate its electronic and superconducting properties, we measured the electrical resistivity, magnetic susceptibility, and de Haas-van Alphen (dHvA) effect at low temperatures cooled to similar to 30mK and in high magnetic fields up to 36 T. The upper critical field (mu H-0(c2) = 0.23 T) determined by the electrical resistivity under the magnetic field and the electron-phonon coupling constant (lambda(ep) = 0.39) estimated from the Debye temperature suggested a weak-coupling BCS-type superconductivity. The dHvA effect measurements mapped the Fermi surface in detail. The dHvA branches with the frequencies of F = 122-2180 T and the effective masses of m*(c) = 0.83-2.4 m(0) (m(0): rest mass of an electron) were observed. These were reasonably explained by the band-structure calculation based on the full potential linearized augmented-plane-wave method within the local density approximation.