On the existence conditions for a fast surface wave

Conditions are obtained for the existence of a fast-moving surface electromagnetic wave (with a speed close to the speed of light in the vacuum) on a flat interface between the vacuum and an isotropic dissipative medium with a permittivity . The interfaces considered include vacuum–seawater, vacuum–metal, vacuum–plasma, and vacuum–dielectric. Conditions for the existence of negligibly damped surface waves are considered for extremely high (vacuum–seawater, vacuum–metal) and very low (vacuum–plasma, vacuum–dielectric) values. It is shown that at least in these two limit cases, the phase wave velocity and the group wave velocity pass synchronously through the speed of light in the vacuum, which can be considered the reason why surface waves exist at the interface between vacuum and a collisionless plasma (with and ) and do not exist at the interface between the vacuum and a weakly absorbing dielectric (with and ). In the first limit case, it is shown that both the phase and group velocities pass at , implying that a surface wave exists at the vacuum-metal interface (with ), but that a surface wave (Zenneck's wave) cannot exist at the vacuum–seawater interface (with ).