Heavy-Electron Formation and Polaron–Bipolaron Transition in the Anharmonic Holstein Model

Abstract

The emergence of the bipolaronic phase and the formation of the heavy-electron state in the anharmonic Holstein model are investigated using the dynamical mean-field theory in combination with the exact diagonalization method. For a weak anharmonicity, it is confirmed that the first-order polaron-bipolaron transition occurs from the observation of a discontinuity in the behavior of several physical quantities. When the anharmonicity is gradually increased, the polaron-bipolaron transition temperature is reduced as well as the critical values of the electron-phonon coupling constant for polaron-bipolaron transition. For a strong anharmonicity, the polaron-bipolaron transition eventually changes to a crossover behavior. The effect of anharmonicity on the formation of the heavy-electron state near the polaron-bipolaron transition and the crossover region is discussed in detail.

Effect of Phonon-Mediated Attraction on the Kondo Phenomenon Emerging from a Vibrating Magnetic Ion

“…In fact, in the filled-skutterudite compound SmOs 4 Sb 12 , the large electronic specific heat coefficient γ has been observed to be almost independent of an applied magnetic field up to about 30 Tesla [1], in sharp contrast to the decrease of γ due to the magnetic field in the conventional heavy-electron materials originating from the traditional Kondo effect emerging from local magnetic moment. The mechanism of rattling-induced heavy-electron state has been theoretically investigated from various viewpoints [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18].…”

Electric dipolar susceptibility of the Anderson-Holstein model

“…Such oscillation with large amplitude is frequently called rattling and it is considered to play crucial roles for the formation of magnetically-robust heavy electron state in SmOs 4 Sb 12 [2]. This peculiar heavyelectron state has been theoretically investigated from various aspects by several groups [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17].Recently, the Kondo effect of a vibrating magnetic ion in a cage has been theoretically discussed on the basis of a two-channel conduction electron system hybridized with a vibrating magnetic ion [18][19][20]. Note here that a vibrating ion inevitably induces electric dipole moment.…”

“…Such oscillation with large amplitude is frequently called rattling and it is considered to play crucial roles for the formation of magnetically-robust heavy electron state in SmOs 4 Sb 12 [2]. This peculiar heavyelectron state has been theoretically investigated from various aspects by several groups [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17].…”