695 research outputs found
Frenkel Excitons in Random Systems With Correlated Gaussian Disorder
Optical absorption spectra of Frenkel excitons in random one-dimensional
systems are presented. Two models of inhomogeneous broadening, arising from a
Gaussian distribution of on-site energies, are considered. In one case the
on-site energies are uncorrelated variables whereas in the second model the
on-site energies are pairwise correlated (dimers). We observe a red shift and a
broadening of the absorption line on increasing the width of the Gaussian
distribution. In the two cases we find that the shift is the same, within our
numerical accuracy, whereas the broadening is larger when dimers are
introduced. The increase of the width of the Gaussian distribution leads to
larger differences between uncorrelated and correlated disordered models. We
suggest that this higher broadening is due to stronger scattering effects from
dimers.Comment: 9 pages, REVTeX 3.0, 3 ps figures. To appear in Physical Review
Alteraciones ultraestructurales del ovario irradiado
En el presente trabajo, hemos descrito las alteraciones que s~ p rcs~ntan en l o~ ovarws de conejas vlrgenes, que han sido radiadas con 1.500 r. en una sola dosis y sacrificadas a intervalos de uno, uno y medio, dos, cuatro, ocho, quince, lrcint.1 y cuarenta y cinco dÃas. Las lesiones han sido estudiadas con el microscopio clcctrón•co y han consistido en procesos alterattvo del óvulo y células foliculares. Estas alteraciones del follculo las hemos descrito en los grupos correspondientes a las conejas sacrificadas durante el primer dia, dla y medio, dus dú• y cuatro dfas, tras la radiación y han consistido en marcada destrucción de los componentes celulares del fol{culo y pérdida total de la zona pe lúcida; en tanto que en los dfas ocho, quince. treinta y cuarenta y cinco desp u~s de la radiación, hemos encontrJdO p10ccsos de forrn~ci ón de falsos cuerpos luteos y formas de reactiv:~cióo folicu lar
Comment on ``Periodic wave functions and number of extended states in random dimer systems'
There are no periodic wave-functions in the RDM but close to the critical
energies there exist periodic envelopes. These envelopes are given by the
non-disordered properties of the system.Comment: RevTex file, 1 page, Comment X. Huang, X. Wu and C. Gong, Phys. Rev.
B 55, 11018 (1997
Graphene nanoring as a tunable source of polarized electrons
We propose a novel spin filter based on a graphene nanoring fabricated above
a ferromagnetic strip. The exchange interaction between the magnetic moments of
the ions in the ferromagnet and the electron spin splits the electronic states,
and gives rise to spin polarization of the conductance and the total electric
current. We demonstrate that both the current and its polarization can be
controlled by a side-gate voltage. This opens the possibility to use the
proposed device as a tunable source of polarized electrons.Comment: 12 pages, 7 figures, accepted in Nanotechnolog
FIBONACCI SUPERLATTICES OF NARROW-GAP III-V SEMICONDUCTORS
We report theoretical electronic structure of Fibonacci superlattices of
narrow-gap III-V semiconductors. Electron dynamics is accurately described
within the envelope-function approximation in a two-band model.
Quasiperiodicity is introduced by considering two different III-V semiconductor
layers and arranging them according to the Fibonacci series along the growth
direction. The resulting energy spectrum is then found by solving exactly the
corresponding effective-mass (Dirac-like) wave equation using tranfer-matrix
techniques. We find that a self-similar electronic spectrum can be seen in the
band structure. Electronic transport properties of samples are also studied and
related to the degree of spatial localization of electronic envelope-functions
via Landauer resistance and Lyapunov coefficient. As a working example, we
consider type II InAs/GaSb superlattices and discuss in detail our results in
this system.Comment: REVTeX 3.0, 16 pages, 8 figures available upon request. To appear in
Semiconductor Science and Technolog
Fluorescence decay in aperiodic Frenkel lattices
We study motion and capture of excitons in self-similar linear systems in
which interstitial traps are arranged according to an aperiodic sequence,
focusing our attention on Fibonacci and Thue-Morse systems as canonical
examples. The decay of the fluorescence intensity following a broadband pulse
excitation is evaluated by solving the microscopic equations of motion of the
Frenkel exciton problem. We find that the average decay is exponential and
depends only on the concentration of traps and the trapping rate. In addition,
we observe small-amplitude oscillations coming from the coupling between the
low-lying mode and a few high-lying modes through the topology of the lattice.
These oscillations are characteristic of each particular arrangement of traps
and they are directly related to the Fourier transform of the underlying
lattice. Our predictions can be then used to determine experimentally the
ordering of traps.Comment: REVTeX 3.0 + 3PostScript Figures + epsf.sty (uuencoded). To appear in
Physical Review
Linear optical properties of one-dimensional Frenkel exciton systems with intersite energy correlations
We analyze the effects of intersite energy correlations on the linear optical
properties of one-dimensional disordered Frenkel exciton systems. The
absorption line width and the factor of radiative rate enhancement are studied
as a function of the correlation length of the disorder. The absorption line
width monotonously approaches the seeding degree of disorder on increasing the
correlation length. On the contrary, the factor of radiative rate enhancement
shows a non-monotonous trend, indicating a complicated scenario of the exciton
localization in correlated systems. The concept of coherently bound molecules
is exploited to explain the numerical results, showing good agreement with
theory. Some recent experiments are discussed in the light of the present
theory.Comment: 18 pages, 3 figues, REVTeX, to appear in Physical Review
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