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Superconductivity in two-band non-adiabatic systems

M. E. Palistrant·V. A. Ursu
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Abstract

Theory of superconductivity in two-band non-adiabatic systems with strong electron correlations in the linear approximation over non-adiabaticity is built in the article. Having assumed weak electron-phonon interaction analytical expressions for the vertex functions and "intersecting " functions for each energy band are obtained. Mass operators of Green functions with account of diagrams with intersection of two lines of electron- phonon interaction (exceeding the frameworks of Migdal theorem) are derived as well as main equations of theory of superconductivity in two-band systems. Analytical formulas for the temperature of superconducting transition Tc are obtained as well as renormalization of the quantities which enter these formulas because of effects of non-adiabaticity and strong electron correlations. Dependence of Tc and coefficient of isotope effect on Migdal parameter m is studied. Overlapping of energy bands on Fermi surface with effects of non-adiabaticity at low values of transferred momentum is shown to obtain high values of Tc even assuming weak electron-phonon interaction.

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M. E. Palistrant, V. A. Ursu. 2006-04-27. Superconductivity in two-band non-adiabatic systems. https://arxiv.org/abs/cond-mat/0602551

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