Heavy fermions in the periodic Anderson model with singlet-triplet crystal-field levels

We investigate the two-orbital periodic Anderson model with f2-configuration by using the dynamical mean-field theory in which the effective impurity Anderson model is solved using the exact diagonalization method. The renormalization factor Z and the local moment are obtained as functions of the Coulomb interaction U, the exchange (Hund's rule) coupling J and the crystal-field splitting Δ. When the ionic ground state is triplet for Δ<Δc=3J, the heavy fermion state with the mass enhancement m*/m=Z-1-bar 100 together with ∼2 is realized in the strong correlation regime for U-bar W, where W is the conduction bandwidth. When the ionic ground state is singlet for Δ-bar Δc, m*/m∼1 and ∼0 for any value of U. When the singlet ground state and the triplet excited state form a quasi-quartet for Δ-bar Δc, the system shows a moderate mass enhancement m*/m∼10-100