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.

@article{Dolgov:1982,
	author = {O. V. Dolgov and E. G. Maksimov},
	title = {Transition temperature of strong-coupling superconductors},
	publisher = {Physics-Uspekhi},
	year = {1982},
	journal = {Phys. Usp.},
	volume = {25},
	number = {9},
	pages = {688-704},
	url = {https://ufn.ru/en/articles/1982/9/c/},
	doi = {10.1070/PU1982v025n09ABEH004602}
}