  The present paper is devoted to the theoretical study of the spectrum of
low-frequency electronic density oscillations running along the boundary of two
contacting two-dimensional electronic systems in the perpendicular magnetic
field. For the first time, such waves were predicted in the Institute of
Radio-engineering and Electronics of RAS (V.A. Volkov, S.A. Mikhailov, 1992),
studied experimentally in the papers of foreign investigations and called
inter-edge magnetoplasmons (IEMP). When the two-dimensional system is finite
and has the half-plane shape, the internal boundary becomes external and these
plasmons go over into the well-known edge magnetoplasmons. The existing theory
of edge and inter-edge magnetoplasmons is built with the neglect of spatial
dispersion of the conductivity. Here we attempt to derive and analyze the IEMP
dispersion equation involving spatial dispersion of conductivity. The inner
boundary is assumed to be a straight line at which the electron concentration
changes weakly but stepwise. The jump of the diagonal conductivity is
considered small compared with that of the Hall magnetoconductivity. The IEMP
frequency is small compared with the cyclotron frequency. The IEMP frequency as
a function of wavevector oscillates with the period determined by a ratio of
electron cyclotron radius to the plasmon wavelength. For long wavelengths, the
IEMP dispersion curve coincides with the known result.
