Effect of Coulomb interaction on the electron spectral density and the transverse conductivity of layered metals

Interaction of electrons with strongly anisotropic plasma oscillations leads to an incoherent contribution to the electron spectral density that does not vanish even for energies distant from the Fermi surface. In the superconducting state, this gives a peak-dip-hump structure analogous to that observed in layered high-$T_c$ superconductors. The incoherent part of the spectral density and electron transitions with the participation of plasmons are responsible for two mechanisms of the occurrence of a finite conductivity in the transverse direction at high voltages or frequencies.