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Phase separation of electrons strongly coupled with phonons in cuprates and manganites | A. S. Alexandrov
; | Date: |
23 Oct 2008 | Abstract: | Recent advanced Monte Carlo simulations have not found superconductivity and
phase separation in the Hubbard model with on-site repulsive electron-electron
correlations. We argue that microscopic phase separations in cuprate
superconductors and colossal magnetoresistance (CMR) manganites originate from
a strong electron-phonon interaction (EPI) combined with unavoidable disorder.
Attractive electron correlations, caused by an almost unretarded EPI, are
sufficient to overcome the direct inter-site Coulomb repulsion in these
charge-transfer Mott-Hubbard insulators, so that low energy physics is that of
small polarons and small bipolarons (real-space electron (hole) pairs dressed
by phonons). They form clusters localised by disorder below the mobility edge,
but propagate as the Bloch states above the mobility edge. I identify the
Froehlich finite-range EPI with optical phonons as the most essential for
pairing and phase separation in superconducting layered cuprates. The pairing
of oxygen holes into heavy bipolarons in the paramagnetic phase
(current-carrier density collapse (CCDC)) explains also CMR of doped manganites
due to magnetic break-up of bipolarons in the ferromagnetic phase. Here I
briefly present an explanation of high and low-resistance phase coexistence
near the ferromagnetic transition as a mixture of polaronic ferromagnetic and
bipolaronic paramagnetic domains due to unavoidable disorder in doped
manganites. | Source: | arXiv, 0810.4277 | Services: | Forum | Review | PDF | Favorites |
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