Abstract
Many cerium-based heavy fermion (HF) compounds have pressure-temperature phase diagrams in which a superconducting region extends far from a magnetic quantum critical point. In at least two compounds, CeCu Si and CeCu Ge , an enhancement of the superconducting transition temperature was found to coincide with an abrupt valence change, with strong circumstantial evidence for pairing mediated by critical valence, or charge transfer, fluctuations. This pairing mechanism, and the valence instability, is a consequence of a f-c Coulomb repulsion term U in the Hamiltonian. While some non-superconducting Ce compounds show a clear first order valence instability, analogous to the Ce α-γ transition, we argue that a weakly first order valence transition may be a general feature of Ce-based HF systems, and both magnetic and critical valence fluctuations may be responsible for the superconductivity in these systems.
Original language | English |
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Article number | 051002 |
Journal | Journal of the Physical Society of Japan |
Volume | 76 |
Issue number | 5 |
DOIs | |
Publication status | Published - 1 May 2007 |