Controlling of exciton condensate by external fields and phonon laser
  The novel method of observation and controlling of Bose-Einstein condensation in the system of spatially and momentum-space indirect excitons in coupled quantum wells using in-plane magnetic and normal electric fields is proposed. Fields are used for exciton dispersion engeneering. In the presence of in-plane magnetic field ground state of spatially indirect exciton becomes also indirect in the momentum space. Manipulation of electric field magnitude is used for tuning to resonance of transition of "dark" long-life spatially and momentum-space indirect exciton in condensate into spatially and momentum-space direct exciton in radiative zone, with phonon creation, and with subsequent recombination of the direct exciton in radiative zone. Recombination rate of indirect excitons in condensate according to proposed scheme sharply rises at resonance. As a result besides enhanced spectral narrow photoluminescence connected with recombination of direct exciton in radiative zone with specific angular dependence, almost monochromatic and unidirectional beam of phonons appears. An opportunity of obtaining of "phonon laser" radiation on the basis of this effect in considered. 
Yu.E.Lozovik, I.V.Ovchinnikov