STRONG INTERACTION OF CORRELATED ELECTRONS WITH PHONONS: EXCHANGE OF PHONON CLOUDS BY POLARONS
Moskalenko V.A., Entel P., Marinaro M., Digor D.F.

Received: January 24, 2003

PACS: 71.10.Fd, 71.27.+a, 71.38.-k

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We investigate the interaction of strongly correlated electrons with phonons in the framework of the Hubbard-Holstein model. The electron-phonon interaction is considered to be strong and is an important parameter of the model in addition to the Coulomb repulsion of electrons and the band filling. This interaction with nondispersive optical phonons is transformed to the problem of mobile polarons using the canonical transformation of Lang and Firsov. We discuss the case where the on-site Coulomb repulsion is exactly canceled by the phonon-mediated attractive interaction. We suggest that polarons exchanging phonon clouds can lead to polaron pairing and superconductivity. The fact that the frequency of the collective mode of phonon clouds is larger than the bare frequency then determines the superconducting transition temperature.