The unusual two-photon emission by Bose-condensed excitons caused by simultaneous recombination of two excitons with opposite momenta leaving the occupation numbers of excitonic states with momenta $\mathbf{p}\ensuremath{\ne}0$ unchanged (below coherent two-exciton recombination) is investigated. Raman scattering accompanied by the analogous two-exciton recombination (or creation) is also analyzed. The excess momentum equal to the change of the electromagnetic field momentum in these processes can be transferred to phonons or impurities. The processes under consideration take place if there is Bose condensation in the interacting exciton system, and, therefore, can be used as a method to reveal exciton Bose condensation. If the frequency of the incident light $\ensuremath{\omega}<2\ensuremath{\Omega}$ $(\ensuremath{\Omega}$ is the frequency corresponding to the recombination of an exciton with p=0), the coherent two-exciton recombination with the excess momentum elastically transferred to impurities leads to the appearance of the spectral line $2\ensuremath{\Omega}\ensuremath{-}\ensuremath{\omega}$ corresponding to the induced two-photon emission. In this case the anti-Stokes line on frequency $\ensuremath{\omega}+2\ensuremath{\Omega}$ also appears in the Raman spectrum. If $\ensuremath{\omega}>2\ensuremath{\Omega},$ there are both Stokes and anti-Stokes lines on frequencies $\ensuremath{\omega}\ifmmode\pm\else\textpm\fi{}2\ensuremath{\Omega}$ in the Raman spectrum. The induced two-photon emission is impossible in this case. The spectral lines mentioned above have phonon replicas on frequencies $|\ensuremath{\omega}\ifmmode\pm\else\textpm\fi{}(2\ensuremath{\Omega}\ensuremath{-}n{\ensuremath{\omega}}_{0}^{s})|$ corresponding to the transmission of the excess momentum (partially or as a whole) to optical phonons of frequency ${\ensuremath{\omega}}_{0}^{s}$ $(n$ is an integer number). The quantitative estimation shows that the light corresponding to the coherent two-exciton recombination can be experimentally observed in ${\mathrm{Cu}}_{2}\mathrm{O}.$ The unusual two-photon emission by Bose-condensed excitons caused by simultaneous recombination of two excitons with opposite momenta leaving the occupation numbers of excitonic states with momenta $\mathbf{p}\ensuremath{\ne}0$ unchanged (below coherent two-exciton recombination) is investigated. Raman scattering accompanied by the analogous two-exciton recombination (or creation) is also analyzed. The excess momentum equal to the change of the electromagnetic field momentum in these processes can be transferred to phonons or impurities. The processes under consideration take place if there is Bose condensation in the interacting exciton system, and, therefore, can be used as a method to reveal exciton Bose condensation. If the frequency of the incident light $\ensuremath{\omega}<2\ensuremath{\Omega}$ $(\ensuremath{\Omega}$ is the frequency corresponding to the recombination of an exciton with p=0), the coherent two-exciton recombination with the excess momentum elastically transferred to impurities leads to the appearance of the spectral line $2\ensuremath{\Omega}\ensuremath{-}\ensuremath{\omega}$ corresponding to the induced two-photon emission. In this case the anti-Stokes line on frequency $\ensuremath{\omega}+2\ensuremath{\Omega}$ also appears in the Raman spectrum. If $\ensuremath{\omega}>2\ensuremath{\Omega},$ there are both Stokes and anti-Stokes lines on frequencies $\ensuremath{\omega}\ifmmode\pm\else\textpm\fi{}2\ensuremath{\Omega}$ in the Raman spectrum. The induced two-photon emission is impossible in this case. The spectral lines mentioned above have phonon replicas on frequencies $|\ensuremath{\omega}\ifmmode\pm\else\textpm\fi{}(2\ensuremath{\Omega}\ensuremath{-}n{\ensuremath{\omega}}_{0}^{s})|$ corresponding to the transmission of the excess momentum (partially or as a whole) to optical phonons of frequency ${\ensuremath{\omega}}_{0}^{s}$ $(n$ is an integer number). The quantitative estimation shows that the light corresponding to the coherent two-exciton recombination can be experimentally observed in ${\mathrm{Cu}}_{2}\mathrm{O}.$

arXiv:cond-mat/9803318Physical review. B, Condensed matterSep 1, 199813 citations

The properties of Bose condensed excitons and biexcitons

S. A. Moskalenko

Aug 1, 19750 citations

Two‐photon resonant Raman scattering via biexcitons

Vu Duy Phach, Albert Bivas, B. Hönerlage +1 more

Abstract Two‐photon resonant Raman scattering processes are studied in different scattering configurations in CuCl. Observation of Raman lines from the front face of the crystal (backward scattering) yields new information on the energy of the transverse T5 exciton and on the biexciton damping. In transmission (forward scattering), two new emission lines can be identified as due to the Raman effect. They show a strong angular dependence because of the polariton nature of the particles involved. Their characteristic features contradict an interpretation in terms of Bose‐Einstein condensed biexcitons.Abstract Two‐photon resonant Raman scattering processes are studied in different scattering configurations in CuCl. Observation of Raman lines from the front face of the crystal (backward scattering) yields new information on the energy of the transverse T5 exciton and on the biexciton damping. In transmission (forward scattering), two new emission lines can be identified as due to the Raman effect. They show a strong angular dependence because of the polariton nature of the particles involved. Their characteristic features contradict an interpretation in terms of Bose‐Einstein condensed biexcitons.

physica status solidi (b)Mar 1, 197858 citations

Bose-Einstein Condensation of Excitons

Claude Benoit à la Guillaume, Erio Tosatti

Europhysics newsJan 1, 19740 citations

(n

is an integer number). The quantitative estimation shows that the light corresponding to the coherent two-exciton recombination can be experimentally observed in

{\mathrm{Cu}}_{2}\mathrm{O}.