1,114 research outputs found
Stress Dependence of Exciton Relaxation Processes in Cu2O
A comprehensive study of the exciton relaxation processes in Cu2O has led to
some surprises. We find that the ortho-para conversion rate becomes slower at
high stress, and that the Auger nonradiative recombination rate increases with
stress, with apparently no Auger recombination at zero stress. These results
have important consequences for the pursuit of Bose-Einstein condensation of
excitons in a harmonic potential.Comment: 10 figures, 1 tabl
Dynamical T-matrix theory for high-density excitons in coupled quantum wells
Excitons in coupled quantum wells open the possibility to reach high
densities close to equilibrium. In a recent experiment employing a lateral trap
potential, a blue shift and a broadening of the exciton emission line has been
seen (Snoke, SSC 134). The standard Hartree-Fock treatment can explain the blue
shift but fails to give a finite broadening. Starting from the (spin-dependent)
many-exciton Hamiltonian with direct and exchange potential, we present a
dynamical T-matrix calculation for the single-exciton Green's function which is
directly related to the frequency- and angle-resolved photoluminescence. The
calculated spectrum is blue shifted and broadened due to exciton-exciton
scattering. At high excitation, both the spectrum and the angular emission are
getting narrow. This is a direct manifestation for off-diagonal long range
order and a precursor of condensation.Comment: 7 pages, 3 figures. Proceedings NOEKS 8 (Muenster 2006
Resonant two-photon excitation of 1s paraexcitons in Cuprous Oxide
We have created paraexcitons in Cuprous Oxide via resonant two-photon
generation, and examined their population dynamics by means of time-correlated
single photon detection. Confining the excitons to a constant volume in a
harmonic potential trap made with inhomogeneous applied stress along the [001]
axis, we find that paraexcitons are created directly, and orthoexcitons appear
primarily through the well-known excitonic Auger process. Hot excitons are also
created via a three-photon process when the IR laser is non-resonant. Also we
generate excitons with two colliding pulses, and the luminescence is weaker
than that from one beam excitation with same total laser power. These results
show that resonant one-beam two-photon generation of paraexcitons is a
promising way to pursue Bose-Einstein condensation of paraexcitons.Comment: 22 pages, 9 figure
Coherence and Optical Emission from Bilayer Exciton Condensates
Experiments aimed at demonstrating Bose-Einstein condensation of excitons in
two types of experiments with bilayer structures (coupled quantum wells) are
reviewed, with an emphasis on the basic effects. Bose-Einstein condensation
implies the existence of a macroscopic coherence, also known as off-diagonal
long-range order, and proposed tests and past claims for coherence in these
excitonic systems are discussed.Comment: 14 pages, 4 figure
Bose-Einstein condensation of excitons in CuO
We present a parameter-free model which estimates the density of excitons in
CuO, related to experiments that have tried to create an excitonic
Bose-Einstein condensate. Our study demonstrates that the triplet-state
excitons move along adiabats and obey classical statistics, while the
singlet-state excitons are a possible candidate for forming a Bose-Einstein
condensate. Finally we show that the results of this study do not change
qualitatively in a two-dimensional exciton gas, which can be realized in a
quantum well.Comment: 6 pages, RevTex, 1 ps figur
- …