742 research outputs found
Collective Dynamics and Strong Pinning near the Onset of Charge Order in LaNdSrCuO
The dynamics of charge-ordered states is one of the key issues in underdoped
cuprate high-temperature superconductors, but static short-range charge-order
(CO) domains have been detected in almost all cuprates. We probe the dynamics
across the CO (and structural) transition in
LaNdSrCuO by measuring nonequilibrium charge
transport, or resistance as the system responds to a change in temperature
and to an applied magnetic field. We find evidence for metastable states,
collective behavior, and criticality. The collective dynamics in the critical
regime indicates strong pinning by disorder. Surprisingly, nonequilibrium
effects, such as avalanches in , are revealed only when the critical region
is approached from the charge-ordered phase. Our results on
LaNdSrCuO provide the long-sought evidence for
the fluctuating order across the CO transition, and also set important
constraints on theories of dynamic stripes.Comment: final version: 5 pages, 3 figures; includes Supplemental Material (3
pages, 7 figures
Current-voltage characteristics and vortex dynamics in highly underdoped LaSrCuO
The temperature dependence of the nonlinear current-voltage (-)
characteristics in highly underdoped LaSrCuO ( and
0.08) thick films has been studied in both zero and perpendicular magnetic
fields . Power-law behavior of is found for both and . The critical current was extracted, and its temperature and
magnetic field dependences were studied in detail. The
Berezinskii-Kosterlitz-Thouless physics dominates the nonlinear - near
the superconducting transition at , and it continues to contribute up to a
characteristic temperature . Nonlinear - persists up to an even
higher temperature due to the depinning of vortices.Comment: 4 pages, 4 figures; Superstripes 2015 conferenc
The influence of gravitational lensing on the spectra of lensed QSOs
We consider the influence of (milli/micro)lensing on the spectra of lensed
QSOs. We propose a method for the observational detection of microlensing in
the spectra of lensed QSOs and apply it to the spectra of the three lensed QSOs
(PG 1115+080, QSO 1413+117 and QSO 0957+561) observed with Hubble Space
Telescope (HST). We find that the flux ratio between images A1 and A2 of PG
1115+080 is wavelength-dependent and shows differential magnification between
the emission lines and the continuum. We interpret this magnification as
arising from millilensing. We also find that the temporal variations in the
continuum of image C of QSO 1413+117 may be caused by microlensing, while the
temporal variation observed in QSO 0957+561 was probably an intrinsic one.Comment: 11 pages, accepted for publication in MNRA
Geometric origin of scaling in large traffic networks
Large scale traffic networks are an indispensable part of contemporary human
mobility and international trade. Networks of airport travel or cargo ships
movements are invaluable for the understanding of human mobility
patterns\cite{Guimera2005}, epidemic spreading\cite{Colizza2006}, global
trade\cite{Imo2006} and spread of invasive species\cite{Ruiz2000}. Universal
features of such networks are necessary ingredients of their description and
can point to important mechanisms of their formation. Different
studies\cite{Barthelemy2010} point to the universal character of some of the
exponents measured in such networks. Here we show that exponents which relate
i) the strength of nodes to their degree and ii) weights of links to degrees of
nodes that they connect have a geometric origin. We present a simple robust
model which exhibits the observed power laws and relates exponents to the
dimensionality of 2D space in which traffic networks are embedded. The model is
studied both analytically and in simulations and the conditions which result
with previously reported exponents are clearly explained. We show that the
relation between weight strength and degree is , the relation
between distance strength and degree is and the relation
between weight of link and degrees of linked nodes is
on the plane 2D surface. We further analyse the
influence of spherical geometry, relevant for the whole planet, on exact values
of these exponents. Our model predicts that these exponents should be found in
future studies of port networks and impose constraints on more refined models
of port networks.Comment: 17 pages, 5 figures, 1 tabl
Mesoscopic Behavior Near a Two-Dimensional Metal-Insulator Transition
We study conductance fluctuations in a two-dimensional electron gas as a
function of chemical potential (or gate voltage) from the strongly insulating
to the metallic regime. Power spectra of the fluctuations decay with two
distinct exponents (1/v_l and 1/v_h). For conductivity , we find a third exponent (1/v_i) in the shortest samples, and
non-monotonic dependence of v_i and v_l on \sigma. We study the dependence of
v_i, v_l, v_h, and the variances of corresponding fluctuations on \sigma,
sample size, and temperature. The anomalies near
indicate that the dielectric response and screening length are critically
behaved, i.e. that Coulomb correlations dominate the physics.Comment: Revised according to referee remark
Optical Emission Lines and the X-Ray Properties of Type 1 Seyfert Galaxies
In this contribution we report on the study of the optical emission lines and
X-ray spectra of a sample of Type 1 AGNs, collected at the Sloan Digital Sky
Survey database and observed by the XMM Newton satellite. Exploiting the
different instruments carried onboard XMM, we identify the spectral components
of the soft and hard energy bands (in the range from 0.3 keV up to 10 keV). The
properties of the X-ray continuum and of the Fe Kalpha line feature are
investigated in relation to the optical broad emission line profiles and
intensity ratios. The resulting picture of emission, absorption and reflection
processes is interpreted by means of a BLR structural model that was developed
on the basis of independent optical and radio observations.Comment: 6 pages, 3 figures, Proceedings of the VIII Serbian Conference on
Spectral Line Shapes in Astrophysics, accepted for publication on Baltic
Astronomy. Corrected typos in V
Tuning from failed superconductor to failed insulator with magnetic field
Do charge modulations compete with electron pairing in high-temperature
copper-oxide superconductors? We investigated this question by suppressing
superconductivity in a stripe-ordered cuprate compound at low temperature with
high magnetic fields. With increasing field, loss of three-dimensional
superconducting order is followed by reentrant two-dimensional
superconductivity and then an ultra-quantum metal phase. Circumstantial
evidence suggests that the latter state is bosonic and associated with the
charge stripes. These results provide experimental support to the theoretical
perspective that local segregation of doped holes and antiferromagnetic spin
correlations underlies the electron-pairing mechanism in cuprates.Comment: 20 pp, 4 figs.; accepted version; for open-access published version,
click on DOI belo
Are Boltzmann Plots of Hydrogen Balmer lines a tool for identifying a subclass of S1 AGN?
It is becoming clear that we can define two different types of nearby AGN
belonging to the Seyfert 1 class (S1), on the basis of the match of the
intensities of their Broad Balmer Lines (BBL) with the Boltzmann Plots (BP).
These two types of S1 galaxies, that we call BP-S1 and NoBP-S1, are
characterized, in first approximation, by Broad Line Regions (BLR) with
different structural and physical properties. In this communication, we show
that these features can be well pointed out by a multi-wavelength analysis of
the continuum and of the broad recombination Hydrogen lines, that we carry out
on a sample of objects detected at optical and X-ray frequencies. The
investigation is addressed to verify whether BP-S1 are the ideal candidates for
the study of the kinematical and structural properties of the BLR, in order to
derive reliable estimates of the mass of their central engine and to constrain
the properties of their nuclear continuum spectrum.Comment: 26 pages, 4 figures (1 multi-paged). Accepted for publication on
Advances in Space Research. Contribution to the IX SCSLS
Detailed Analysis of Balmer Lines in a Sloan Digital Sky Survey Sample of 90 Broad Line Active Galactic Nuclei
In order to contribute to the general effort aiming at the improvement of our
knowledge about the physical conditions within the Broad Line Region (BLR) of
Active Galactic Nuclei (AGN), here we present the results achieved by our
analysis of the spectral properties of a sample of 90 broad line emitting
sources, collected at the Sloan Digital Sky Survey (SDSS) database. By focusing
our attention mainly onto the Balmer series of hydrogen emission lines, which
is the dominant feature in the optical wavelength range of many BLR spectra, we
extracted several flux and profile measurements, which we related to other
source properties, such as optical continuum luminosities, inferred black hole
masses, and accretion rates. Using the Boltzmann Plot method to investigate the
Balmer line flux ratios as a function of the line profiles, we found that
broader line emitting AGN typically have larger H_alpha / H_beta and smaller
H_gamma / H_beta and H_delta / H_beta line ratios. With the help of some recent
investigations, we model the structure of the BLR and we study the influence of
the accretion process on the properties of the BLR plasma.Comment: 14 pages, 11 figures, fixes the wrong names of 4 objects; published
on Ap
- …