Electron sound of finite amplitude in superconductors

The paper attempts to demonstrate the existence of sinusoidal electron sound of finite amplitude in superconductors. It is shown that perturbations of this type can exist at finite temperatures when the superconductor is a two-component system composed of a superconducting condensate and normal excitations. The normal component, which contributes to the electron sound, moves collisionlessly in antiphase with the superfluid component, screening to a considerable extent the electric fields formed by the superfluid component. At low amplitudes, electron sound is strongly damped due to interaction with normal excitations (Landau damping). Electron sound waves exist in the critical temperature range, when the concentration of normal excitations is large enough to ensure screening.