caa a22 4500 467911010 CHVBK 20180406152849.0 cr unu---uuuuu 170328e20061001xx s 000 0 eng 10.1007/s11232-006-0127-0 doi (NATIONALLICENCE)springer-10.1007/s11232-006-0127-0 Two-band superconductivity theory beyond the Migdal theorem [Elektronische Daten] [M. Palistrant, V. Ursu] We propose a superconductivity theory of two-band nonadiabatic systems with strong electron correlations in the linear approximation in nonadiabaticity. Assuming a weak electron-phonon interaction, we obtain analytic expressions for the vertex and "intersecting” functions for each of the two bands. With the diagrams involving intersections of two electron-phonon interaction lines taken into account (which means going beyond the Migdal theorem), we determine mass operators of the Green's functions and use them to derive the basic equations of the superconductivity theory for two-band systems. We find an analytic expression for the superconducting transition temperature Tc that differs from the expression in the case of the standard two-band systems by an essential renormalization of the relevant quantities that results from the nonadiabaticity effects and strong electron correlations. We study the dependence of Tc and of the isotopic coefficient α on the Migdal parameter m = ω0/εF and show that accounting for the overlap of energy bands on the Fermi surface and for the nonadiabaticity effects at small values of the transferred momentum (q ≪ 2pF) allows obtaining high values of Tc even for the weak electron-phonon interaction. Springer Science+Business Media, Inc., 2006 superconductivity nationallicence nonadiabatic system nationallicence electron-phonon interaction nationallicence Migdal theorem nationallicence Palistrant M. Institute of Applied Physics, Academy of Sciences of Moldova, Chisinau, Moldova aut Ursu V. Institute of Applied Physics, Academy of Sciences of Moldova, Chisinau, Moldova aut Theoretical and Mathematical Physics Kluwer Academic Publishers-Consultants Bureau 149/1(2006-10-01), 1393-1406 0040-5779 149:1<1393 2006 149 11232 https://doi.org/10.1007/s11232-006-0127-0 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s11232-006-0127-0 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Palistrant M. Institute of Applied Physics, Academy of Sciences of Moldova, Chisinau, Moldova aut NATIONALLICENCE 700 1- Ursu V. Institute of Applied Physics, Academy of Sciences of Moldova, Chisinau, Moldova aut NATIONALLICENCE 773 0- Theoretical and Mathematical Physics Kluwer Academic Publishers-Consultants Bureau 149/1(2006-10-01), 1393-1406 0040-5779 149:1<1393 2006 149 11232 Metadata rights reserved Springer special CC-BY-NC licence nationallicence SWISSBIB 467911010 BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer