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Signatures of valence fluctuations in CeCu2Si2 under high pressure

A. T. Holmes·D. Jaccard·K. Miyake
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Abstract

Simultaneous resistivity and a.c.-specific heat measurements have been performed under pressure on single crystalline CeCu2Si2 to over 6 GPa in a hydrostatic helium pressure medium. A series of anomalies were observed around the pressure coinciding with a maximum in the superconducting critical temperature, $T_c^{max}$. These anomalies can be linked with an abrupt change of the Ce valence, and suggest a second quantum critical point at a pressure $P_v \simeq 4.5$ GPa, where critical valence fluctuations provide the superconducting pairing mechanism, as opposed to spin fluctuations at ambient pressure. Such a valence instability, and associated superconductivity, is predicted by an extended Anderson lattice model with Coulomb repulsion between the conduction and f-electrons. We explain the T-linear resistivity found at $P_v$ in this picture, while other anomalies found around $P_v$ can be qualitatively understood using the same model.

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A. T. Holmes, D. Jaccard, K. Miyake. 2003-06-03. Signatures of valence fluctuations in CeCu2Si2 under high pressure. https://doi.org/10.1103/physrevb.69.024508

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