Valence Instability and Superconductivity in Heavy Fermion Systems

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, 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.

11 pages, 16 figures

References in corpus (2)

• Signatures of valence fluctuations in CeCu2Si2 under high pressure
• Superconductivity emerging near quantum critical point of valence transition

Cited by in corpus (4)

• The quantum critical point in CeRhIn_5: a resistivity study
• Thermal conductivity evidence for d_{x^2-y^2} pairing symmetry in the heavy-fermion CeIrIn5 superconductor
• Magneto-transport properties governed by the antiferromagnetic fluctuations in heavy fermion superconductor CeIrIn${}_5$
• A precursor state to unconventional superconductivity in CeIrIn${}_5$