  We consider effective interactions in a 2D hybrid polariton- electron system
and calculate dispersion of elementary excitations accounting the spin degree
of freedom of the particles. Due to the crucial role played by the exchange
term in polariton- electron interactions the dispersions of this system become
spin- dependent and show unusual behavior. The coupling of the excitations of
the condensate with 2D plasmon can result in appearence of roton minimum in the
dispersion and destruction of the condensate for close enough situated quantum
wells with electrons and excitons.
