Valence Instability and the Quantum Critical Point in an Extended Periodic Anderson Model: Analysis Based on the Dynamical Mean Field Theory

The dynamical mean field theory combined with exact diagonalization is used to study the valence instability in an extended periodic Anderson model. It is found that at fixed total electron number, the f-electron number is rapidly decreased against the f-electron level epsilon((0))(f) in the presence of the repulsive interaction U-cf between a conduction electron and an f electron. This implies the enhancement of valence fluctuations due to U-cf. In addition, a first-order valence transition is likely to occur, provided the c-f mixing is small and U-cf is large enough to be comparable to the band width of conduction electrons. The quantum critical point of valence transition is identified in the epsilon((0))(f)-U-cf plane. Implications for the valence fluctuations of the related Ce compounds are also discussed.