Transition temperature of strong-coupling superconductors
O.V. Dolgov a, b
E.G. Maksimov a
a Lebedev Physical Institute, Russian Academy of Sciences, Leninsky prosp. 53, Moscow, 119991, Russian Federation
b Max-Planck Institut für Festkörperforschung, Stuttgart, Germany
The possible existence of superconductors with high transition temperatures is analyzed for both the ordinary electron-phonon interaction and nonphonon superconductivity mechanisms. The existence of such systems depends on a negative static dielectric permittivity. The possible occurrence of this situation for an electron-ion system is analyzed. It is shown that negative values of the static dielectric permittivity are possible in the case of strong local-field effects, i. e., in the case of exchange-correlation interactions in the electron subsystem or the localization of point ions for an electron-phonon system. Equations for the transition temperature of strong-coupling superconductors are analyzed. Restrictions imposed on the transition temperature by the equations themselves and by the conditions for stability of the material are examined.