Herein, the dynamics of excitons coupled with optical phonons in a triangular system is numerically studied. By representing the excitons by quasi-spin states, the similarity between the chiral spin states and the exciton chiral states is discussed. In particular, the optical control of excitons is discussed, where photoirradiation causes the switching of the exciton states on the ultrafast time scale by Raman scattering. A phase diagram is obtained based on the ground-state properties of the system determined by the magnitudes of the exciton-phonon interactions and exciton transfer energy. By varying the frequency and/or intensity of light, a transition between exciton-phonon composite states is induced, which suggests the possibility of the coherent control of the chiral properties of excitonic systems via phonon excitation.Herein, the dynamics of excitons coupled with optical phonons in a triangular system is numerically studied. By representing the excitons by quasi-spin states, the similarity between the chiral spin states and the exciton chiral states is discussed. In particular, the optical control of excitons is discussed, where photoirradiation causes the switching of the exciton states on the ultrafast time scale by Raman scattering. A phase diagram is obtained based on the ground-state properties of the system determined by the magnitudes of the exciton-phonon interactions and exciton transfer energy. By varying the frequency and/or intensity of light, a transition between exciton-phonon composite states is induced, which suggests the possibility of the coherent control of the chiral properties of excitonic systems via phonon excitation.

arXiv:2305.18182May 29, 20230 citations

Condensed excitons in quantum wells: temperature effects

V. I. Sugakov

Physics of the Solid StateJan 1, 20060 citations

Quantum Kinetics of the Exciton Bose-Einstein Condensation

H. Haug

Photo-excited excitons, i.e. closely bound electron-hole pairs, are in the low-density regime approximately bosons. For sufficiently low temperatures and sufficiently high densities of the exciton gas, a nonequilibrium phase transition in the form of a Bose-Einstein condensation (BEC) can be expected. Various levels of the description of the kinetics of relaxation and condensation due to the coupling of the excitons to a cold reservoir of acoustic phonons are discussed. For noninteracting excitons a rate equation approach with the exciton Boltzmann equation can be used. For interacting excitons the nonmarkovian quantum kinetics is required for the description of the BEC in order to incorporate the changes of the energy spectrum during the condensation self-consistently. Finally colored Langevin fluctuations can be used to calculate the phase diffusion of the condensate.Photo-excited excitons, i.e. closely bound electron-hole pairs, are in the low-density regime approximately bosons. For sufficiently low temperatures and sufficiently high densities of the exciton gas, a nonequilibrium phase transition in the form of a Bose-Einstein condensation (BEC) can be expected. Various levels of the description of the kinetics of relaxation and condensation due to the coupling of the excitons to a cold reservoir of acoustic phonons are discussed. For noninteracting excitons a rate equation approach with the exciton Boltzmann equation can be used. For interacting excitons the nonmarkovian quantum kinetics is required for the description of the BEC in order to incorporate the changes of the energy spectrum during the condensation self-consistently. Finally colored Langevin fluctuations can be used to calculate the phase diffusion of the condensate.

Phase TransitionsJan 1, 20021 citation

Manifestation of exciton Bose condensation in induced two-phonon emission and Raman scattering

Yu. E. Lozovik, Andrei V. Poushnov

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

(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}.