  Binary complex plasmas consist of microparticles of two different species and
can form two-dimensional square lattices under certain conditions. The
dispersion relations of the square lattice waves are derived for the
longitudinal and transverse in-plane modes, assuming that the out-of-plane mode
is suppressed by the strong vertical confinement. The results are compared with
the spectra obtained in Langevin dynamics simulations. Furthermore, we
investigate the dependence of the dispersion relation on the charge ratio and
mass ratio of the two particle species.
