Low-Energy Electronic Collective Modes and Superconductivity in Layered Systems

The Coulomb interaction induces low-energy electronic collective modes (LEECM) in layered conductors. We study how the superconducting critical temperature T_c is affected by such collective modes within the strong-coupling theory of superconductivity. Whereas we account for both the electron–phonon and the screened Coulomb interactions, the main focus is set on the latter. The dielectric function is displayed and screening within RPA is discussed. We then show that LEECM affect the superconducting state constructively in layered structures. Their effect can be interpreted as a negative * in the Eliashberg theory. We examine in what respect the collective-mode scenario differs in layered conductors as compared to three-dimensional (3D) isotropic metals.