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College Park, Maryland      June 6 - 10 , 2004

T2-D3 (2:15 PM): Crystalline Electric Field Effects in CeMIn5: Superconductivity and the Influence of Kondo Spin Fluctuations

A. D. Christianson (University of California at Irvine), E. D. Bauer (Los Alamos National Laboratory), J. M. Lawrence (University of California at Irvine), P. S. Riseborough (Temple University, Philadelphia, Pennsylvania 19122), N. O. Moreno, P. G. Pagliuso, J. L. Sarrao, J. D. Thompson, M. P. Hehlen, F. R. Trouw (Los Alamos National Laboratory), E. A. Goremychkin (Argonne National Laboratory), R. J. McQueeney (LANL and Iowa State University, Ames, Iowa 50011)

We have measured the crystalline electric field excitations (CEF) of the CeMIn5 (M = Co, Rh, Ir) series of heavy fermion superconductors by means of inelastic neutron scattering (INS). Fits to a CEF model reproduce the INS spectra and the high temperature magnetic susceptibility. The CEF parameters, energy level splittings, and wavefunctions are tabulated for each member of the CeMIn5 series and compared to each other as well as to the results of previous measurements. 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. In each case, the CEF excitations are observed as broad lines in the INS spectrum. We attribute this broadening to Kondo hybridization of the localized f moments with the conduction electrons. The evolution of the superconducting transition temperatures in the different members of CeMIn5 can then be understood as a direct consequence of the strength of this hybridization. Due to the importance of Kondo spin fluctuations in these materials, we also present calculations within the non-crossing approximation to the Anderson impurity model including the effect of CEF level splitting for the INS spectra and the magnetic susceptibility.

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