Pomeranchuk effect in unstable Ytterbium systems

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YbInCu₄ and its alloys present discontinuous, first order iso-structural transitions at pressure dependent temperatures Tᵥ(P), where a local moment phase coexist with a renormalized Fermi liquid phase. We show that along the coexistence line Tᵥ(P) the entropy of the large volume renormalized Fermi liquid phase is smaller than that of the higher density, local moment phase. This implies the existence of a Pomeranchuk effect in these Kondo lattice materials in analogy with ³He. The theoretical possibility of using these systems as cooling machines is discussed.