High-temperature superconductivity from realistic Coulomb and Fröhlich interactions

¹ Instituto de Fisica “Gleb Wataghin”, Universidade Estadual de Campinas - UNICAMP 13083-970, Campinas, São Paulo, Brasil
² Department of Physics, Loughborough University - Loughborough LE11 3TU, UK, EU
³ Dipartimento di Fisica “E.R. Caianiello”, Università degli Studi di Salerno - I-84084 Fisciano (SA), Italy, EU

^(a) j.h.samson@lboro.ac.uk

Received: 23 July 2012
Accepted: 13 September 2012

Abstract

In recent years ample experimental evidence has shown that charge carriers in high-temperature superconductors are strongly correlated but also coupled with lattice vibrations (phonons), signalling that the true origin of high-T_c superconductivity can only be found in a proper combination of Coulomb and electron-phonon interactions. On this basis, we propose and study a model for high-T_c superconductivity which accounts for realistic Coulomb repulsion, strong electron-phonon (Fröhlich) interaction and residual on-site (Hubbard-) correlations without any ad hoc assumptions on their relative strength and interaction range. In the framework of this model, which exhibits a phase transition to a superconducting state with a critical temperature T_c well in excess of 100 K, we emphasize the role of as the driving parameter for a BEC/BCS crossover. Our model lays a microscopic foundation for the polaron-bipolaron theory of superconductivity. We argue that the high-T_c phenomenon originates in competing Coulomb and Fröhlich interactions beyond the conventional BCS description.