Crystalline electric field effects in CeMIn<inf>5</inf> (M=Co,Rh,Ir): Superconductivity and the influence of Kondo spin fluctuations

Abstract

We have measured the crystalline electric field (CEF) excitations of the CeMIn5 (M=Co,Rh,Ir) series of heavy fermion superconductors by means of inelastic neutron scattering. In each case, the CEF excitations are considerably broadened, due to Kondo hybridization of the localized f-moments with the conduction electrons. Fits to a phenomenological CEF model reproduce the inelastic neutron scattering spectra and the high-temperature magnetic susceptibility. We also present calculations within the noncrossing approximation (NCA) to the Anderson impurity model, including the effect of CEF level-splitting for the inelastic neutron scattering spectra and the magnetic susceptibility. Our results indicate that the CEF level-splitting in all three materials is similar, and can be thought of as being derived from the cubic parent compound CeIn3. in which an excited state quartet at ∼12 meV is split into two doublets by the lower symmetry of the tetragonal environment of the CeMIn5 materials. The evolution of the superconducting transition temperatures in the different members of CeMIn 5 can be understood as a direct consequence of the strength of the 4f-conduction electron hybridization.