Superconducting and Fermi Surface Properties of a Valence Fluctuation Compound CeIr₂

To investigate the superconducting and the electronic properties of CeIr2 which was reported as a valence fluctuation compound with the superconducting transition temperature of Tc ~0.3 K, we measured the electrical resistivity, the magnetic susceptibility, and the de Haasvan Alphen (dHvA) effect at low temperatures down to ~30 mK and in high magnetic fields up to 36 T. The upper critical field 0Hc2 = 0.23 T determined by the electrical resistivity under the magnetic field as well as the electron-phonon coupling constant ep = 0.39 estimated from the Debye temperature suggest that the superconductivity is a weak-coupling BCS-type.The dHvA effect measurements mapped the Fermi surface in detail, in which the dHvA branches with the frequencies of F = (122 ~ 2180) T and the effective masses of mc * = (0.83~2.4)m0 (m0: rest mass of an electron) were observed, which were reasonably well explained by the band structure calculation based on a full potential linearized augmented-plane-wave (FLAPW) method within the local density approximation (LDA).