Abstract
Simultaneous resistivity and ac specific heat measurements have been performed under pressure on single-crystalline to over 6 GPa in a hydrostatic helium pressure medium. A series of anomalies was observed around the pressure coinciding with a maximum in the superconducting critical temperature, These anomalies can be linked with an abrupt change of the Ce valence and suggest a second quantum critical point at a pressure 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 in this picture, while other anomalies found around can be qualitatively understood using the same model.
- Received 30 May 2003
DOI:https://doi.org/10.1103/PhysRevB.69.024508
©2004 American Physical Society