32,543 research outputs found
Kinetics of photoinduced ordering in azo-dye films: two-state and diffusion models
We study the kinetics of photoinduced ordering in the azo-dye SD1
photoaligning layers and present the results of modeling performed using two
different phenomenological approaches. A phenomenological two state model is
deduced from the master equation for an ensemble of two-level molecular
systems. Using an alternative approach, we formulate the two-dimensional (2D)
diffusion model as the free energy Fokker-Planck equation simplified for the
limiting regime of purely in-plane reorientation. The models are employed to
interpret the irradiation time dependence of the absorption order parameters
extracted from the available experimental data by using the exact solution to
the light transmission problem for a biaxially anisotropic absorbing layer. The
transient photoinduced structures are found to be biaxially anisotropic whereas
the photosteady and the initial states are uniaxial.Comment: revtex4, 34 pages, 9 figure
Graphene-based Josephson junction single photon detector
We propose to use graphene-based Josephson junctions (gJjs) to detect single
photons in a wide electromagnetic spectrum from visible to radio frequencies.
Our approach takes advantage of the exceptionally low electronic heat capacity
of monolayer graphene and its constricted thermal conductance to its phonon
degrees of freedom. Such a system could provide high sensitivity photon
detection required for research areas including quantum information processing
and radio-astronomy. As an example, we present our device concepts for gJj
single photon detectors in both the microwave and infrared regimes. The dark
count rate and intrinsic quantum efficiency are computed based on parameters
from a measured gJj, demonstrating feasibility within existing technologies.Comment: 11 pages, 6 figures, and 1 table in the main tex
Transport properties of a periodically driven superconducting single electron transistor
We discuss coherent transport of Cooper pairs through a Cooper pair shuttle.
We analyze both the DC and AC Josephson effect in the two limiting cases where
the charging energy is either much larger or much smaller than the
Josephson coupling . In the limit we present the detailed
behavior of the critical current as a function of the damping rates and the
dynamical phases. The AC effect in this regime is very sensitive to all
dynamical scales present in the problem. The effect of fluctuations of the
external periodic driving is discussed as well. In the opposite regime the
system can be mapped onto the quantum kicked rotator, a classically chaotic
system. We investigate the transport properties also in this regime showing
that the underlying classical chaotic dynamics emerges as an incoherent
transfer of Cooper pairs through the shuttle. For an appropriate choice of the
parameters the Cooper pair shuttle can exhibit the phenomenon of dynamical
localization. We discuss in details the properties of the localized regime as a
function of the phase difference between the superconducting electrodes and the
decoherence due to gate voltage fluctuations. Finally we point how dynamical
localization is reflected in the noise properties of the shuttle.Comment: 22 pages, 7 figures; v3 (published version): added references,
improved readabilit
Stretched exponential relaxation in a diffusive lattice model
We studied the single dimer dynamics in a lattice diffusive model as a
function of particle density in the high densification regime. The mean square
displacement is found to be subdiffusive both in one and two dimensions. The
spatial dependence of the self part of the van Hove correlation function
displays as function of a single peak and signals a dramatic slow down of
the system for high density. The self intermediate scattering function is
fitted to the Kohlrausch-Williams-Watts law. The exponent extracted
from the fits is density independent while the relaxation time follows a
scaling law with an exponent 2.5.Comment: 5 pages, 3 figures, to be published in Phys. Rev.
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