2,379 research outputs found
Google matrix of the citation network of Physical Review
We study the statistical properties of spectrum and eigenstates of the Google
matrix of the citation network of Physical Review for the period 1893 - 2009.
The main fraction of complex eigenvalues with largest modulus is determined
numerically by different methods based on high precision computations with up
to binary digits that allows to resolve hard numerical problems for
small eigenvalues. The nearly nilpotent matrix structure allows to obtain a
semi-analytical computation of eigenvalues. We find that the spectrum is
characterized by the fractal Weyl law with a fractal dimension .
It is found that the majority of eigenvectors are located in a localized phase.
The statistical distribution of articles in the PageRank-CheiRank plane is
established providing a better understanding of information flows on the
network. The concept of ImpactRank is proposed to determine an influence domain
of a given article. We also discuss the properties of random matrix models of
Perron-Frobenius operators.Comment: 25 pages. 17 figures. Published in Phys. Rev.
Temperature evolution of the quantum Hall effect in the FISDW state: Theory vs Experiment
We discuss the temperature dependence of the Hall conductivity
in the magnetic-field-induced spin-density-wave (FISDW) state of the
quasi-one-dimensional Bechgaard salts (TMTSF)_2X. Electronic thermal
excitations across the FISDW energy gap progressively destroy the quantum Hall
effect, so interpolates between the quantized value at zero
temperature and zero value at the transition temperature T_c, where FISDW
disappears. This temperature dependence is similar to that of the superfluid
density in the BCS theory of superconductivity. More precisely, it is the same
as the temperature dependence of the Fr\"ohlich condensate density of a regular
CDW/SDW. This suggests a two-fluid picture of the quantum Hall effect, where
the Hall conductivity of the condensate is quantized, but the condensate
fraction of the total electron density decreases with increasing temperature.
The theory appears to agree with the experimental results obtained by measuring
all three components of the resistivity tensor simultaneously on a
(TMTSF)_2PF_6 sample and then reconstructing the conductivity tensor.Comment: 3 pages, 2 figures, submitted to the proceedings of International
Workshop on Electronic Crystals (ECRYS-99
Proximity effect thermometer for local temperature measurements on mesoscopic samples
Using the strong temperature dependent resistance of a normal metal wire in
proximity to a superconductor, we have been able to measure the local
temperature of electrons heated by flowing a dc current in a metallic wire to
within a few tens of millikelvin at low temperatures. By placing two such
thermometers at different parts of a sample, we have been able to measure the
temperature difference induced by a dc current flowing in the sample. This
technique may provide a flexible means of making quantitative thermal and
thermoelectric measurements on mesoscopic metallic samples
Positive exchange bias in ferromagnetic La0.67Sr0.33MnO3 / SrRuO3 bilayers
Epitaxial La0.67Sr0.33MnO3 (LSMO)/ SrRuO3 (SRO) ferromagnetic bilayers have
been grown on (001) SrTiO3 (STO) substrates by pulsed laser deposition with
atomic layer control. We observe a shift in the magnetic hysteresis loop of the
LSMO layer in the same direction as the applied biasing field (positive
exchange bias). The effect is not present above the Curie temperature of the
SRO layer (), and its magnitude increases rapidly as the temperature is lowered
below . The direction of the shift is consistent with an antiferromagnetic
exchange coupling between the ferromagnetic LSMO layer and the ferromagnetic
SRO layer. We propose that atomic layer charge transfer modifies the electronic
state at the interface, resulting in the observed antiferromagnetic interfacial
exchange coupling.Comment: accepted to Applied Physics Letter
Evolution of transport properties of BaFe2-xRuxAs2 in a wide range of isovalent Ru substitution
The effects of isovalent Ru substitution at the Fe sites of BaFe2-xRuxAs2 are
investigated by measuring resistivity and Hall coefficient on high-quality
single crystals in a wide range of doping (0 < x < 1.4). Ru substitution
weakens the antiferromagnetic (AFM) order, inducing superconductivity for
relatively high doping level of 0.4 < x < 0.9. Near the AFM phase boundary, the
transport properties show non-Fermi-liquid-like behaviors with a
linear-temperature dependence of resistivity and a strong temperature
dependence of Hall coefficient with a sign change. Upon higher doping, however,
both of them recover conventional Fermi-liquid behaviors. Strong doping
dependence of Hall coefficient together with a small magnetoresistance suggest
that the anomalous transport properties can be explained in terms of
anisotropic charge carrier scattering due to interband AFM fluctuations rather
than a conventional multi-band scenario.Comment: 7 pages, 6 figures, submitted to Phys. Rev.
Quantum Hall Ferromagnetism in a Two-Dimensional Electron System
Experiments on a nearly spin degenerate two-dimensional electron system
reveals unusual hysteretic and relaxational transport in the fractional quantum
Hall effect regime. The transition between the spin-polarized (with fill
fraction ) and spin-unpolarized () states is accompanied
by a complicated series of hysteresis loops reminiscent of a classical
ferromagnet. In correlation with the hysteresis, magnetoresistance can either
grow or decay logarithmically in time with remarkable persistence and does not
saturate. In contrast to the established models of relaxation, the relaxation
rate exhibits an anomalous divergence as temperature is reduced. These results
indicate the presence of novel two-dimensional ferromagnetism with a
complicated magnetic domain dynamic.Comment: 15 pages, 5 figure
Coexistence of superconductivity and ferromagnetism in two dimensions
Ferromagnetism is usually considered to be incompatible with conventional
superconductivity, as it destroys the singlet correlations responsible for the
pairing interaction. Superconductivity and ferromagnetism are known to coexist
in only a few bulk rare-earth materials. Here we report evidence for their
coexistence in a two-dimensional system: the interface between two bulk
insulators, LaAlO (LAO) and SrTiO (STO), a system that has been studied
intensively recently. Magnetoresistance, Hall and electric-field dependence
measurements suggest that there are two distinct bands of charge carriers that
contribute to the interface conductivity. The sensitivity of properties of the
interface to an electric field make this a fascinating system for the study of
the interplay between superconductivity and magnetism.Comment: 4 pages, 4 figure
Are better conducting molecules more rigid?
We investigate the electronic origin of the bending stiffness of conducting
molecules. It is found that the bending stiffness associated with electronic
motion, which we refer to as electro-stiffness, , is governed by
the molecular orbital overlap and the gap width between HOMO and LUMO
levels, and behaves as . To study the
effect of doping, we analyze the electron filling-fraction dependence on
and show that doped molecules are more flexible. In addition, to
estimate the contribution of to the total stiffness, we consider
molecules under a voltage bias, and study the length contraction ratio as a
function of the voltage. The molecules are shown to be contracted or dilated,
with increasing nonlinearly with the applied bias
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