A heavy-fermion state with singular density of states

The metamagnetic behavior of CeRu2Si2 and the non Fermi-liquid behavior of CeNi2Ge2 are described by the periodic Coqblin-Schrieffer model with anisot ropic c-f exchange interaction in the mean-field theory. Only the Kramers d oublet of M-J = +/-5/2 for the 4f states of Ce ions is considered, for the case of which the density of quasi-particle states has singularity of \omeg a\(-1/2) around the effective f-level energy. In the asymmetric case applic able to CeRu2Si2, the chemical potential reaches the singularity at a finit e magnetic field, at which the magnetization shows a metamagnetic-like incr ease. On the other hand, in the symmetric case applicable to CeNi2Ge2: the chemical potential is on the singularity at zero magnetic field, and non-Fe rmi-liquid-like behaviors emerge in the susceptibility and the specific hea t.