期刊
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN
卷 76, 期 5, 页码 -出版社
PHYSICAL SOC JAPAN
DOI: 10.1143/JPSJ.76.051002
关键词
heavy fermion superconductors; mixed valence compounds; CeCu2Si2; CeCu2Ge2; superconductivity; fluctuations in superconductors; critical valence fluctuations; new paradigm
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, CeCu2Si2 and CeCu2Ge2, 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-fc in the Hamiltonian. While some non-superconducting Ce compounds show a clear first order valence instability, analogous to the Ce alpha-gamma 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.
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