Coexistence of two Bose-Einstein condensates of two-dimensional magnetoexcitons. Exciton-plasmon collective elementary excitations

Possibility of the Bose-Einstein condensation of magnetic excitons in an ideal two-dimensional system in a strong perpendicular magnetic field is investigated theoretically taking into account the influence of virtual transitions to the excited Landau levels and Anderson-type coherent excited states. It was understood, that the Bose-Einstein condensed (BEC-ed) magnetoexcitons with considerable wave vector K and motional dipole moment Kl2, where l is the magnetic length, can form the droplets of the metastable dielectric liquid phase, whereas the BEC-ed magnetoexcitons with K =0 can form a stable degenerate Bose-gas surrounding the droplet. We have shown that collective elementary excitations of the BEC of excitons are mixed with plasma oscillations of the electron-hole system in the presence of strong perpendicular magnetic field. Their mutual influence is determined by the coherence factor and essentially depends on the condensate wave vector K.