Dynamical and statistical behaviors of Frenkel excitons in a matter system consisting of N two-level-atoms and interacting with an external field are studied with the molecular field and random phase approximations. Existence of a phase transition is suggested both in the exciton system and exciton-photon coupled system. This phase transition is the second order transition whose order parameter is the polarizability. A new type of condensation of the photon-exciton coupled wave, in which a macroscopic number of excitons and photons participate, has been found as a result of appreciable contribution of photons to the phase transition. When the incident light is coherent, the condition of phase transition is modified by photon induced exciton-exciton interaction. The energy dispersion of elementary excitations is derived.Dynamical and statistical behaviors of Frenkel excitons in a matter system consisting of N two-level-atoms and interacting with an external field are studied with the molecular field and random phase approximations. Existence of a phase transition is suggested both in the exciton system and exciton-photon coupled system. This phase transition is the second order transition whose order parameter is the polarizability. A new type of condensation of the photon-exciton coupled wave, in which a macroscopic number of excitons and photons participate, has been found as a result of appreciable contribution of photons to the phase transition. When the incident light is coherent, the condition of phase transition is modified by photon induced exciton-exciton interaction. The energy dispersion of elementary excitations is derived.

Journal of the Physical Society of JapanDec 1, 19770 citations

Ultrafast Phase Relaxation of Excitons via Exciton-Exciton and Exciton-Electron Collisions

Lothar Schultheis, J. Kühl, A. Honold +1 more

The ultrafast relaxation of excitons in GaAs, coherently excited by a short optical pulse and subjected to collisions with free carriers and noncoherent excitons which are independently created by a second synchronized light pulse, is studied directly in the time domain by a probing of the excitonic phase coherence. The relaxation rates reveal strong exciton-exciton scattering with a collision efficiency of 1.6 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{3}$ ${\mathrm{s}}^{\ensuremath{-}1}$ and even 10 times more efficient exciton-free-carrier scattering.The ultrafast relaxation of excitons in GaAs, coherently excited by a short optical pulse and subjected to collisions with free carriers and noncoherent excitons which are independently created by a second synchronized light pulse, is studied directly in the time domain by a probing of the excitonic phase coherence. The relaxation rates reveal strong exciton-exciton scattering with a collision efficiency of 1.6 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}4}$ ${\mathrm{cm}}^{3}$ ${\mathrm{s}}^{\ensuremath{-}1}$ and even 10 times more efficient exciton-free-carrier scattering.

Physical Review LettersSep 29, 1986303 citations

Excitons

Karl W. Böer, Udo W. Pohl

Springer eBooksJan 1, 20238 citations

Exciton condensation in strongly correlated electron bilayers

Louk Rademaker, Jeroen van den Brink, Jan Zaanen +1 more

We studied the possibility of exciton condensation in Mott insulating bilayers. In these strongly correlated systems, an exciton is the bound state of a double occupied and empty site. In the strong coupling limit, the exciton acts as a hard-core boson. Its physics is captured by the exciton $t$ - $J$ model, containing an effective $XXZ$ model describing the exciton dynamics only. Using numerical simulations and analytical mean-field theory, we constructed the ground-state phase diagram. Three homogeneous phases can be distinguished: the antiferromagnet, the exciton checkerboard crystal, and the exciton superfluid. For most model parameters, however, we predict macroscopic phase separation between these phases. The exciton superfluid exists only for large exciton hopping energy. Additionally, we studied the collective modes and susceptibilities of the three phases. In the superfluid phase, we find the striking feature that the bandwidth of the spin-triplet excitations, potentially detectable by resonant inelastic x-ray scattering (RIXS), is proportional to the superfluid density. The superfluid phase mode is visible in the charge susceptibility, measurable by RIXS or electron energy loss spectroscopy (EELS).We studied the possibility of exciton condensation in Mott insulating bilayers. In these strongly correlated systems, an exciton is the bound state of a double occupied and empty site. In the strong coupling limit, the exciton acts as a hard-core boson. Its physics is captured by the exciton $t$-$J$ model, containing an effective $XXZ$ model describing the exciton dynamics only. Using numerical simulations and analytical mean-field theory, we constructed the ground-state phase diagram. Three homogeneous phases can be distinguished: the antiferromagnet, the exciton checkerboard crystal, and the exciton superfluid. For most model parameters, however, we predict macroscopic phase separation between these phases. The exciton superfluid exists only for large exciton hopping energy. Additionally, we studied the collective modes and susceptibilities of the three phases. In the superfluid phase, we find the striking feature that the bandwidth of the spin-triplet excitations, potentially detectable by resonant inelastic x-ray scattering (RIXS), is proportional to the superfluid density. The superfluid phase mode is visible in the charge susceptibility, measurable by RIXS or electron energy loss spectroscopy (EELS).

arXiv:1310.0685Physical Review BDec 26, 201321 citations

A phase formalism for excitonic transitions

M. Grado-Caffaro, M. Grado-Caffaro

OptikJul 1, 20053 citations

{\mathrm{cm}}^{3}

${\mathrm{s}}^{\ensuremath{-}1}$ and even 10 times more efficient exciton-free-carrier scattering.

t

J

model, containing an effective

XXZ

model describing the exciton dynamics only. Using numerical simulations and analytical mean-field theory, we constructed the ground-state phase diagram. Three homogeneous phases can be distinguished: the antiferromagnet, the exciton checkerboard crystal, and the exciton superfluid. For most model parameters, however, we predict macroscopic phase separation between these phases. The exciton superfluid exists only for large exciton hopping energy. Additionally, we studied the collective modes and susceptibilities of the three phases. In the superfluid phase, we find the striking feature that the bandwidth of the spin-triplet excitations, potentially detectable by resonant inelastic x-ray scattering (RIXS), is proportional to the superfluid density. The superfluid phase mode is visible in the charge susceptibility, measurable by RIXS or electron energy loss spectroscopy (EELS).