  We have analytically studied plasmons in an electron system comprised of two
spatially separated layers -- an infinite two-dimensional electron system
(2DES) and a 2D strip. Our analysis reveals the existence of plasmon modes that
are localized near and propagate along the strip. These modes are characterized
by the wave vector in the direction of the strip, as well as the number of
charge density nodes, N, across the strip. In the long-wavelength limit, the
fundamental mode N=0 is found to have gapless linear dispersion. When the
external perpendicular magnetic field is applied, this mode remains gapless and
exhibits peculiar magnetodispersion. We analyze the correlation between our
findings and the previously established results on plasmons in gated and
partially gated 2DESs.
