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 Kl(2), 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. (c) 2004 Elsevier Ltd. All rights reserved.