Magnetic-field induced quantum critical points of valence transition in Ce- and Yb-based heavy fermions

The mechanism of how the magnetic field controls the critical end point of the first-order valence transition is clarified, which is essentially ascribed to charge degrees of freedom. It is shown that the quantum critical point is induced by applying the magnetic field, which explains a peculiar magnetic response in CeIrIn₅ and sharp contrast between X=Ag and Cd for YbXCu₄. Significance of the proximity of the first-order valence transition in the Ce- and Yb-based heavy fermions is pointed out.