Kondo effect emerging from a spin-vibronic state

Abstract

We discuss the Kondo effect in an electron system dynamically coupled with local Jahn-Teller phonons. For the purpose, we consider the two-orbital Anderson model including both Coulomb interactions and the coupling between electrons and Jahn-Teller phonons on an impurity site. Note that in this paper, we consider a quarter-filling case. First we analyze a local problem and confirm a spin-vibronic quartet ground state, characterized by the direct product of spin and vibronic degrees of freedom. Next we include the hybridization term and analyze the model by using a numerical renormalization group method. From the evaluation of entropy, specific heat, and several kinds of susceptibilities, it is found that spin and total angular momenta are simultaneously screened by conduction electrons, leading to the Kondo phenomenon due to the entropy release of ln 4 of the local spin-vibronic state. A possibility of heavy-electron formation in the spin-vibronic Kondo effect is briefly discussed.