3,001 research outputs found
Thermal broadening of the J-band in disordered linear molecular aggregates: A theoretical study
We theoretically study the temperature dependence of the J-band width in
disordered linear molecular aggregates, caused by dephasing of the exciton
states due to scattering on vibrations of the host matrix. In particular, we
consider inelastic one- and two-phonon scattering between different exciton
states (energy-relaxation-induced dephasing), as well as elastic two-phonon
scattering of the excitons (pure dephasing). The exciton states follow from
numerical diagonalization of a Frenkel Hamiltonian with diagonal disorder; the
scattering rates between them are obtained using the Fermi Golden Rule. A
Debye-like model for the one- and two-phonon spectral densities is used in the
calculations. We find that, owing to the disorder, the dephasing rates of the
individual exciton states are distributed over a wide range of values. We also
demonstrate that the dominant channel of two-phonon scattering is not the
elastic one, as is often tacitly assumed, but rather comes from a similar
two-phonon inelastic scattering process. In order to study the temperature
dependence of the J-band width, we simulate the absorption spectrum, accounting
for the dephasing induced broadening of the exciton states. We find a power-law
(T^p) temperature scaling of the effective homogeneous width, with an exponent
p that depends on the shape of the spectral density of host vibrations. In
particular, for a Debye model of vibrations, we find p ~ 4, which is in good
agreement with experimental data on J-aggregates of pseudoisocyanine [J. Phys.
Chem. A 101, 7977 (1997)].Comment: 14 pages, 7 figure
DNA double helices for single molecule electronics
The combination of self-assembly and electronic properties as well as its
true nanoscale dimensions make DNA a promising candidate for a building block
of single molecule electronics. We argue that the intrinsic double helix
conformation of the DNA strands provides a possibility to drive the electric
current through the DNA by the perpendicular electric (gating) field. The
transistor effect in the poly(G)-poly(C) synthetic DNA is demonstrated within a
simple model approach. We put forward experimental setups to observe the
predicted effect and discuss possible device applications of DNA. In
particular, we propose a design of the single molecule analog of the Esaki
diode.Comment: 4 pages, 4 figur
Photon recoil momentum in a Bose-Einstein condensate of a dilute gas
We develop a "minimal" microscopic model to describe a
two-pulse-Ramsay-interferometer-based scheme of measurement of the photon
recoil momentum in a Bose-Einstein condensate of a dilute gas [Campbell et al.,
Phys. Rev. Lett. 94, 170403 (2005)]. We exploit the truncated coupled
Maxwell-Schroedinger equations to elaborate the problem. Our approach provides
a theoretical tool to reproduce essential features of the experimental results.
Additionally, we enable to calculate the quantum-mechanical mean value of the
recoil momentum and its statistical distribution that provides a detailed
information about the recoil event.Comment: 6 pages, 4 figure
Explicit asymptotic velocity of the boundary between particles and antiparticles
On the real line initially there are infinite number of particles on the
positive half-line., each having one of negative velocities
. Similarly, there are infinite number of
antiparticles on the negative half-line, each having one of positive
velocities . Each particle moves with constant
speed, initially prescribed to it. When particle and antiparticle collide, they
both disappear. It is the only interaction in the system. We find explicitly
the large time asymptotics of - the coordinate of the last collision
before between particle and antiparticle.Comment: 25 page
Decoherence of Excitons in Multichromophore Systems: Thermal Line Broadening and Destruction of Superradiant Emission
We study the temperature-dependent dephasing rate of excitons in chains of
chromophores, accounting for scattering on static disorder as well as acoustic
phonons in the host matrix. From this we find a powerlaw temperature dependence
of the absorption line width, in excellent quantitative agreement with
experiments on dye aggregates. We also propose a relation between the line
width and the exciton coherence length imposed by the phonons. The results
indicate that the much debated steep rise of the fluorescence lifetime of
pseudo-isocyanine aggregates above 40 K results from the fact that this
coherence length drops below the localization length imposed by static
disorder.Comment: 4 pages, 2 figure
FPT-algorithms for some problems related to integer programming
In this paper, we present FPT-algorithms for special cases of the shortest
lattice vector, integer linear programming, and simplex width computation
problems, when matrices included in the problems' formulations are near square.
The parameter is the maximum absolute value of rank minors of the corresponding
matrices. Additionally, we present FPT-algorithms with respect to the same
parameter for the problems, when the matrices have no singular rank
sub-matrices.Comment: arXiv admin note: text overlap with arXiv:1710.00321 From author:
some minor corrections has been don
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