Enhanced Kondo Effect in an Electron System Dynamically Coupled with Local Optical Phonon(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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We discuss Kondo behavior of a conduction electron system coupled with local optical phonon by analyzing the Anderson-Holstein model with the use of a numerical renormalization group (NRG) method. There appear three typical regions due to the balance between Coulomb interaction U_<ee> and phonon-mediated attraction U_<ph>. For U_<ee>>U_<ph>, we observe the standard Kondo effect concerning spin degree of freedom. Since the Coulomb interaction is effectively reduced as U_<ee>-U_<ph>, the Kondo temperature T_K is increased when U_<ph> is increased. On the other hand, for U_<ee><U_<ph>, there occurs the Kondo effect concerning charge degree of freedom, since vacant and double occupied states play roles of pseudo-spins. Note that in this case, T_K is decreased with the increase of U_<ph>. Namely, T_K should be maximized for U_<ee>≈U_<ph>. Then, we analyze in detail the Kondo behavior at U_<ee>=U_<ph>, which is found to be explained by the polaron Anderson model with reduced hybridization of polaron and residual repulsive interaction among polarons. By comparing the NRG results of the polaron Anderson model with those of the original Anderson-Holstein model, we clarify the Kondo behavior in the competing region of U_<ee>≈U_<ph>.
社団法人日本物理学会の論文
2007-08-15