High-frequency polariton waves at the metal-vacuum interface

Some new aspects of the problem on linear electromagnetic plasma oscillations at the plane metal-vacuum interface are studied. The analysis is made by using Maxwell equations for electric and magnetic fields supplemented with an equation for hydrodynamics of electron plasma of the metal. This set of equations allow the existence of previously undiscussed specific long-wave inhomogeneous oscillational eigenstates of polariton type (E-waves) with frequencies of the order of the plasma frequency wp of conduction electrons. For these states the magnetic oscillations are polarized within the interface plane and are perpendicular to the direction of their propagation along the interface. Such waves are due to the hybridization of longitudinal waves of the electron density (plasmons) of the metal and transverse oscillational modes (photons) of the metal and vacuum at the metal-vacuum interface. It is shown that the plasmon excitation in the metal bulk is followed by the initiation of an electromagnetic wave which is localized near the surface and consists of the mixture of metal and vacuum photons. Such an inhomogeneous wave has the dispersion law for bulk plasmons and occurs within their typical frequency band faceωp < omega <√ 2ωp, the typical values of the localization parameter being of the order of c/omegap (c (c is the velocity of light in vacuum). For standard metals this parameter is 10-50 nm. So, such oscillational states may be quite essential in the description of electromagnetic resonances and radiation effects in metal nanostructures