Probing the Kondo Lattice

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We present a phenomenological solution of the Kondo lattice that is derived from an analysis of the bulk specific heat and spin susceptibility of the heavy electron superconductor CeCoIn5. We find that below a crossover temperature corresponding to the intersite coupling scale, T* 45 K, the Kondo gas (of non-interacting Kondo impurities) partially condenses into a heavy electron "Kondo" liquid that has a temperature independent Wilson ratio = 2.0. The relative fraction, f, of the "condensed" Kondo liquid component plays the role of an order parameter; it increases linearly with decreasing temperature until it saturates at its low temperature value of 0.9. The resistivity is shown to be simply the product of (1-f) and that of an isolated Kondo impurity. The generality of this result is suggested by the corresponding analysis for Ce1-xLaxCoIn5 and CeIrIn5.