UNITARY TRANSFORMATION SCHEME FOR POLARON AND BIPOLARON CORRELATION MODELS

On the basis of the modified Lang-Firsov-transformed Holstein-Hubbard model, effective polaron and bipolaron models are derived within the u nified framework of Schrieffer-Wolff-type transformations in the stron g correlation limit. The resulting polaronic t-J and bipolaronic local pairing models obtained for large positive and negative on-site inter actions, respectively, exhibit different renormalizations of the hoppi ng and interaction terms in the moderately heavy and light polaron and bipolaron cases.