13,641 research outputs found
Charge Transport Properties of a Metal-free Phthalocyanine Discotic Liquid Crystal
Discotic liquid crystals can self-align to form one-dimensional
semiconducting wires, many tens of microns long. In this letter, we describe
the preparation of semiconducting films where the stacking direction of the
disc-like molecules is perpendicular to the substrate surface. We present
measurements of the charge carrier mobility, applying temperature-dependent
time-of-flight transient photoconductivity, space-charge limited current
measurements, and field-effect mobility measurements. We provide experimental
verification of the highly anisotropic nature of semiconducting films of
discotic liquid crystals, with charge carrier mobilities of up to
2.8x10cm/Vs. These properties make discotics an interesting choice
for applications such as organic photovoltaics.Comment: 5 pages, 5 figure
Multifractality: generic property of eigenstates of 2D disordered metals.
The distribution function of local amplitudes of eigenstates of a
two-dimensional disordered metal is calculated. Although the distribution of
comparatively small amplitudes is governed by laws similar to those known from
the random matrix theory, its decay at larger amplitudes is non-universal and
much slower. This leads to the multifractal behavior of inverse participation
numbers at any disorder. From the formal point of view, the multifractality
originates from non-trivial saddle-point solutions of supersymmetric
-model used in calculations.Comment: 4 two-column pages, no figures, submitted to PRL
Determination of hadronic partial widths for scalar-isoscalar resonances f0(980), f0(1300), f0(1500), f_0(1750) and the broad state f0(1530^{+90}_{-250})
In the article of V.V. Anisovich et al., Yad. Fiz. 63, 1489 (2000), the
K-matrix solutions for the wave IJ^{PC}=00^{++} were obtained in the mass
region 450 - 1900 MeV where four resonances f0(980), f0(1300), f0(1500),
f0(1750) and the broad state f0(1530^{+90}_{-250}) are located. Based on these
solutions, we determine partial widths for scalar-isoscalar states decaying
into the channels pi-pi, K-anti K, eta-eta, eta-eta', pi-pi-pi-pi and
corresponding decay couplings.Comment: Some typos were correcte
Statistics of delay times in mesoscopic systems as a manifestation of eigenfunction fluctuations
We reveal a general explicit relation between the statistics of delay times
in one-channel reflection from a mesoscopic sample of any spatial dimension and
the statistics of the eigenfunction intensities in its closed counterpart. This
opens a possibility to use experimentally measurable delay times as a sensitive
probe of eigenfunction fluctuations. For the particular case of quasi-one
dimensional geometry of the sample we use an alternative technique to derive
the probability density of partial delay times for any number of open channels.Comment: 12 pages; published version with updated reference
Global Persistence in Directed Percolation
We consider a directed percolation process at its critical point. The
probability that the deviation of the global order parameter with respect to
its average has not changed its sign between 0 and t decays with t as a power
law. In space dimensions d<4 the global persistence exponent theta_p that
characterizes this decay is theta_p=2 while for d<4 its value is increased to
first order in epsilon = 4-d. Combining a method developed by Majumdar and Sire
with renormalization group techniques we compute the correction to theta_p to
first order in epsilon. The global persistence exponent is found to be a new
and independent exponent. We finally compare our results with existing
simulations.Comment: 15 pages, LaTeX, one .eps figure include
Spontaneous Symmetry Breaking in Directed Percolation with Many Colors: Differentiation of Species in the Gribov Process
A general field theoretic model of directed percolation with many colors that
is equivalent to a population model (Gribov process) with many species near
their extinction thresholds is presented. It is shown that the multicritical
behavior is always described by the well known exponents of Reggeon field
theory. In addition this universal model shows an instability that leads in
general to a total asymmetry between each pair of species of a cooperative
society.Comment: 4 pages, 2 Postscript figures, uses multicol.sty, submitte
A graviton propagator for inflation
We construct the scalar and graviton propagator in quasi de Sitter space up
to first order in the slow roll parameter . After
a rescaling, the propagators are similar to those in de Sitter space with an
correction to the effective mass. The limit
corresponds to the E(3) vacuum that breaks de Sitter symmetry, but does not
break spatial isotropy and homogeneity. The new propagators allow for a
self-consistent, dynamical study of quantum back-reaction effects during
inflation.Comment: 23 page
Unveiling the anatomy of mode-coupling theory
The mode-coupling theory of the glass transition (MCT) has been at the
forefront of fundamental glass research for decades, yet the theory's
underlying approximations remain obscure. Here we quantify and critically
assess the effect of each MCT approximation separately. Using Brownian dynamics
simulations, we compute the memory kernel predicted by MCT after each
approximation in its derivation, and compare it with the exact one. We find
that some often-criticized approximations are in fact very accurate, while the
opposite is true for others, providing new guiding cues for further theory
development
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