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Strong-coupling expansions for the anharmonic Holstein model and for the Holstein-Hubbard model

J. K. Freericks·G. D. Mahan
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Abstract

A strong-coupling expansion is applied to the anharmonic Holstein model and to the Holstein-Hubbard model through fourth order in the hopping matrix element. Mean-field theory is then employed to determine transition temperatures of the effective (pseudospin) Hamiltonian. We find that anharmonic effects are not easily mimicked by an on-site Coulomb repulsion, and that anharmonicity strongly favors superconductivity relative to charge-density-wave order. Surprisingly, the phase diagram is strongly modified by relatively small values of the anharmonicity.

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J. K. Freericks, G. D. Mahan. 1996-04-01. Strong-coupling expansions for the anharmonic Holstein model and for the Holstein-Hubbard model. https://doi.org/10.1103/physrevb.54.9372

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