Landau Renormalizations of Superfluid Density in the Heavy-Fermion Superconductor CeCoIn5

Abstract

The formation of heavy-fermion bands can occur by means of the conversion of a periodic array of local moments into itinerant electrons via the Kondo effect and the huge consequent Fermi-liquid renormalizations. Leggett predicted for liquid He3 that Fermi-liquid renormalizations change in the superconducting state, leading to a temperature dependence of the London penetration depth Λ quite different from that in BCS theory. Using Leggett’s theory, as modified for heavy fermions, it is possible to extract from the measured temperature dependence of Λ in high quality samples both Landau parameters F0s and F1s; this has never been accomplished before. A modification of the temperature dependence of the electronic specific heat Cel, related to that of Λ, is also expected. We have carefully determined the magnitude and temperature dependence of Λ in CeCoIn5 by muon spin relaxation rate measurements to obtain F0s=36±1 and F1s=1.2±0.3, and we find a consistent change in the temperature dependence of Cel. This, the first determination of F1s with a value ≪F0s in a heavy-fermion compound, tests the basic assumption of the theory of heavy fermions, that the frequency dependence of the self-energy is much more important than its momentum dependence.

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