Exciton Bose condensate control and the phonon laser

S. A. Moskalenko, Vyacheslav R. Misko, V. Gh. Pavlov

Masudul Haque

Eiichi Hanamura

H. K. Avetissian, A. K. Avetissian, G. F. Mkrtchian +1 more

The collective decay of excitons from initial Bose-Einstein condensate state is investigated theoretically. As a practically more interesting case we consider excitons of the yellow series in the semiconductor cuprous oxide where we have collective photon and phonon-assisted decay of excitons. It is shown that because of intrinsic instability of recoilless two-boson decay of Bose-Einstein condensate, the spontaneously emitted bosonic pairs are amplified, leading to an exponential buildup of a macroscopic population into the certain modes. The collective decay rate has a nonlinear dependence on the excitonic density being comparable or larger than the Auger recombination loss rate up to the high densities, which makes obtainable its observation. The phenomenon considered can also be applied for the realization of a phonon laser.

Michael R. Andrews

Wei-Juan Zhao, P. Stenius, Ataç İmamoğlu

We study the kinetics of condensation in a trapped two-dimensional exciton gas using the quantum Boltzmann equation. We assume that the exciton gas interacts with a lattice that is kept at a constant temperature. Our simulations allow us to estimate and compare the condensation time for Bose gases with and without interactions. We find that anti-Stokes Raman-type two-phonon processes dominate the relaxation rate of low-energy states for a noninteracting gas. The presence of dissipation from the low-energy states results in a heating effect for the exciton gas which in turn increases the mean number of Bose particles required for the onset of condensation. Our results indicate that the condensation time scale in trapped two-dimensional excitons is determined by the phonon emission rate into the ground state. This time scale is orders of magnitude shorter than what is predicted for three-dimensional excitons. The steady state in a dissipative gas is a nonequilibrium condensate, or equivalently an exciton matter laser, where the exciton temperature remains above the lattice temperature.