Physical review. B, Condensed matter
Strong-coupling expansions for the attractive Holstein and Hubbard models
James K. Freericks
Abstract
A strong-coupling expansion for the Holstein (electron-phonon) model is carried out through fourth order. In the large-frequency limit the expansion agrees with known results for the attractive Hubbard model. Mean-field theory is employed to determine transition temperatures of the effective (pseudospin) Hamiltonian and the results are compared with recent Monte Carlo simulations of these models in infinite dimensions.