108 research outputs found
Hyperspherical theory of anisotropic exciton
A new approach to the theory of anisotropic exciton based on Fock
transformation, i.e., on a stereographic projection of the momentum to the unit
4-dimensional (4D) sphere, is developed. Hyperspherical functions are used as a
basis of the perturbation theory. The binding energies, wave functions and
oscillator strengths of elongated as well as flattened excitons are obtained
numerically. It is shown that with an increase of the anisotropy degree the
oscillator strengths are markedly redistributed between optically active and
formerly inactive states, making the latter optically active. An approximate
analytical solution of the anisotropic exciton problem taking into account the
angular momentum conserving terms is obtained. This solution gives the binding
energies of moderately anisotropic exciton with a good accuracy and provides a
useful qualitative description of the energy level evolution.Comment: 23 pages, 8 figure
Bose-Einstein Condensation of Excitons: Reply to Tikhodeev's Criticism
The extended version of our reply to Comment on ``Critical Velocities in
Exciton Superfluidity'' by S. G. Tikhodeev (Phys. Rev. Lett., 84 (2000), 3502
or from http://prl.aps.org/) is presented here. The principal question is
discussed: does the moving exciton-phonon packet contain the coherent
`nucleus', or the exciton-phonon condensate?Comment: 3 pages in LaTe
Nonlinear dynamics of polariton scattering in semiconductor microcavity: bistability vs stimulated scattering
We demonstrate experimentally an unusual behavior of the parametric polariton
scattering in semiconductor microcavity under a strong cw resonant excitation.
The maximum of the scattered signal above the threshold of stimulated
parametric scattering does not shift along the microcavity lower polariton
branch with the change of pump detuning or angle of incidence but is stuck
around the normal direction. We show theoretically that such a behavior can be
modelled numerically by a system of Maxwell and nonlinear Schroedinger
equations for cavity polaritons and explained via the competition between the
bistability of a driven nonlinear MC polariton and the instabilities of
parametric polariton-polariton scattering.Comment: 5 pages, 4 Postscript figures; corrected typo
Relation between inelastic electron tunneling and vibrational excitation of single adsorbates on metal surfaces
We analyse theoretically a relation between the vibrational generation rate
of a single adsorbate by tunneling electrons and the inelastic tunneling (IET)
current in scanning tunneling microscope, and the influence of the vibrational
excitations on the rate of adsorbate motions. Special attention is paid to the
effects of finite lifetime of the vibrational excitations. We show that in the
vicinity and below the IET threshold the rate of adsorbate motion deviates from
a simple power-law dependence on the bias voltage due to the effects of bath
temperature and adsorbate vibrational lifetime broadenings. The temperature
broadening appears to be confined near the threshold voltage within a narrow
region of several , whereas the lifetime broadening manifests itself in
a much wider region of applied voltages below the IET threshold.Comment: 8 pages including 4 figure
Influence of disorder on a Bragg microcavity
Using the resonant-state expansion for leaky optical modes of a planar Bragg
microcavity, we investigate the influence of disorder on its fundamental cavity
mode. We model the disorder by randomly varying the thickness of the Bragg-pair
slabs (composing the mirrors) and the cavity, and calculate the resonant energy
and linewidth of each disordered microcavity exactly, comparing the results
with the resonant-state expansion for a large basis set and within its first
and second orders of perturbation theory. We show that random shifts of
interfaces cause a growth of the inhomogeneous broadening of the fundamental
mode that is proportional to the magnitude of disorder. Simultaneously, the
quality factor of the microcavity decreases inversely proportional to the
square of the magnitude of disorder. We also find that first-order perturbation
theory works very accurately up to a reasonably large disorder magnitude,
especially for calculating the resonance energy, which allows us to derive
qualitatively the scaling of the microcavity properties with disorder strength.Comment: 19 pages, 9 figure
Analytical normalization of resonant states in photonic crystal slabs and periodic arrays of nanoantennas at oblique incidence
We present an analytical formulation for the normalization of resonant states at oblique incidence in one- and
two-dimensional periodic structures with top and bottom boundaries to homogeneous space, such as photonic
crystal slabs and arrays of nanoantennas. The normalization is validated by comparing the resonant state expansion using one and two resonant states with numerically exact results. The predicted changes of resonance frequency and linewidth due to perturbations of refractive index or geometry can be used to study resonantly enhanced refractive index sensing as well as the influence of disorder. In addition, the normalization is essential for the calculation of the Purcell factor
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