Ubiquity of unconventional phenomena observed in a series of heavy fermionmetals is discussed on the basis of an idea of critical valence fluctuations.After surveying experimental aspects of these unconventional behaviors inprototypical compounds, CeCu_2(Si,Ge)_2, under pressure, we propose that sharpvalence crossover phenomena are realized in CeCu_6, CeRhIn_5, and Ce(Ir,Rh)Si_3by tuning the pressure and the magnetic field simultaneously, on the basis ofprevious results for an extended Anderson lattice model with the Coulombrepulsion U_fc between localized f-electron and itinerant conduction electrons.
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