Evolution of the superconducting critical temperature

in Yb-substituted CeCoIn5

Lei Shu

Fudan University, Shanghai, China


    The extraordinary correlated electron phenomena found in intermetallic compounds containing lanthanide ions with an unstable valence (Ce, Pr, Sm, Eu, Tm, Yb) can be traced to the hybridization of localized 4f and conduction electron states. The physics underlying the correlated electron phenomena is associated with the Kondo effect for moderate hybridization in which the valence (4f shell occupation) is nearly integral and “valence fluctuations” for strong hybridization where the valence is nonintegral. In this talk, we describe recent muon spin relaxation, x-ray diffraction, electrical resistivity, magnetic susceptibility, and specific heat measurements on the superconducting heavy fermion system Ce1-xYbxCoIn5 which reveal that the correlated electron state is stabilized throughout the range 0 ≤ x ≤ 0.8, apparently due to cooperative behavior of Ce and Yb ions involving their unstable valences [1]. Phase separation occurs for x > 0.8. Interestingly, the superconducting critical temperature decreases linearly with x from 2.3 K at x = 0 towards 0 K at x = 1. Non-Fermi liquid behavior that varies with x is observed at low temperature, although there is no readily identifiable quantum critical point. The strongly intermediate valence state of Yb in Ce1-xYbxCoIn5 has recently been verified by angle resolved photoemission spectroscopy (ARPES), extended x-ray absorption fine structure (EXAFS), and x-ray absorption near-edge structure (XANES) measurements [2,3]. Measurements of the pressure dependence of the normal state electrical resistivity and superconducting critical temperature as a function of x will be presented. The behavior of CeCoIn5 substituted with Yb is compared to the behavior of CeCoIn5 substituted with other lanthanides.


[1] L. Shu, R. E. Baumbach, M. Janoschek, E. Gonzales, K. Huang, T. A. Sayles, J. Paglione, J. O’Brien, D. A. Zocco, P.-C. Ho, C. A. McElroy, M. B. Maple, Phys. Rev. Lett. 106, 156403 (2011).

[2] C. H. Booth et al., Phys. Rev. B 83, 235117 (2011).

[3] L. Dudy, J. D. Denlinger, L. Shu, M. Janoschek, J. W. Allen, M. B. Maple, in preparation.

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