A. S. Alexandrov, J. H. Samson, G. Sica
In highly polarisable ionic lattices the bare long-range Coulomb repulsion and the attraction mediated by the electron-phonon Fr\"ohlich interaction almost negate each other in the static limit giving rise to the short-range polaronic t-Jp model. This model exhibits a phase transition to a superconducting state with a critical temperature Tc well in excess of 100K [A. S. Alexandrov, EPL 95, 27004 (2011)]. Here we take into account the residual on-site repulsion of polarons (Hubbard-\tilde{U}) in the t-Jp model. The effect of \tilde{U} is double: limiting on-site double occupancy it reduces the inter-site polaron exchange Jp, and gives rise to the BEC/BCS crossover. Our polaronic t-Jp-\tilde{U} model, defined through the bare material parameters, accounts for major electron-electron and electron-phonon correlations providing a microscopic explanation of the high-Tc phenomenon.
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http://arxiv.org/abs/1205.3436
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