1,599 research outputs found
Determining topological order from a local ground state correlation function
Topological insulators are physically distinguishable from normal insulators
only near edges and defects, while in the bulk there is no clear signature to
their topological order. In this work we show that the Z index of topological
insulators and the Z index of the integer quantum Hall effect manifest
themselves locally. We do so by providing an algorithm for determining these
indices from a local equal time ground-state correlation function at any
convenient boundary conditions. Our procedure is unaffected by the presence of
disorder and can be naturally generalized to include weak interactions. The
locality of these topological indices implies bulk-edge correspondence theorem.Comment: 7 pages, 3 figures. Major changes: the paper was divided into
sections, the locality of the order in 3D topological insulators is also
discusse
Removing staggered fermionic matter in U(N) and SU(N) lattice gauge theories
Gauge theories, through the local symmetry which is in their core, exhibit
many local constraints, that must be taken care of and addressed in any
calculation. In the Hamiltonian picture this is phrased through the Gauss laws,
local constraints that restrict the physical Hilbert space and relate the
matter and gauge degrees of freedom. In this work, we present a way that uses
all the Gauss laws in lattice gauge theories with staggered fermions for
completely removing the matter degrees of freedom, at the cost of locally
extending the interaction range, breaking the symmetry and introducing new
local constraints, due to the finiteness of the original local matter spaces
Pulse-Bandwidth Dependence of Coherent Phase Control of Resonance-Mediated (2+1) Three-Photon Absorption
We study in detail coherent phase control of femtosecond resonance-mediated
(2+1) three-photon absorption and its dependence on the spectral bandwidth of
the excitation pulse. The regime is the weak-field regime of third perturbative
order. The corresponding interference mechanism involves a group of
three-photon excitation pathways that are on resonance with the intermediate
state and a group of three-photon excitation pathways that are near resonant
with it. The model system of the study is atomic sodium (Na), for which
experimental and numerical-theoretical results are obtained. Prominent among
the results is our finding that with simple proper pulse shaping an increase in
the excitation bandwidth leads to a corresponding increase in the enhancement
of the three-photon absorption over the absorption induced by the (unshaped)
transform-limited pulse. For example, here, a 40-nm bandwidth leads to an
order-of-magnitude enhancement over the transform-limited absorption.Comment: 23 pages, 5 figure
Topological Wilson-loop area law manifested using a superposition of loops
We introduce a new topological effect involving interference of two meson
loops, manifesting a path-independent topological area dependence. The effect
also draws a connection between quark confinement, Wilson-loops and topological
interference effects. Although this is only a gedanken experiment in the
context of particle physics, such an experiment may be realized and used as a
tool to test confinement effects and phase transitions in quantum simulation of
dynamic gauge theories.Comment: Superceding arXiv:1206.2021v1 [quant-ph
Multiresolution community detection for megascale networks by information-based replica correlations
We use a Potts model community detection algorithm to accurately and
quantitatively evaluate the hierarchical or multiresolution structure of a
graph. Our multiresolution algorithm calculates correlations among multiple
copies ("replicas") of the same graph over a range of resolutions. Significant
multiresolution structures are identified by strongly correlated replicas. The
average normalized mutual information, the variation of information, and other
measures in principle give a quantitative estimate of the "best" resolutions
and indicate the relative strength of the structures in the graph. Because the
method is based on information comparisons, it can in principle be used with
any community detection model that can examine multiple resolutions. Our
approach may be extended to other optimization problems. As a local measure,
our Potts model avoids the "resolution limit" that affects other popular
models. With this model, our community detection algorithm has an accuracy that
ranks among the best of currently available methods. Using it, we can examine
graphs over 40 million nodes and more than one billion edges. We further report
that the multiresolution variant of our algorithm can solve systems of at least
200000 nodes and 10 million edges on a single processor with exceptionally high
accuracy. For typical cases, we find a super-linear scaling, O(L^{1.3}) for
community detection and O(L^{1.3} log N) for the multiresolution algorithm
where L is the number of edges and N is the number of nodes in the system.Comment: 19 pages, 14 figures, published version with minor change
Modulation and correlations lengths in systems with competing interactions
We examine correlation functions in the presence of competing long and short
ranged interactions to find multiple correlation and modulation lengths. We
calculate the ground state stripe width of an Ising ferromagnet, frustrated by
an arbitrary long range interaction. In large systems, we demonstrate that
for a short range system frustrated by a general competing long range
interaction, the crossover temperature veers towards the critical
temperature of the unfrustrated short range system (i.e., that in which the
frustrating long range interaction is removed). We also show that apart from
certain special crossover points, the total number of correlation and
modulation lengths remains conserved. We derive an expression for the change in
modulation length with temperature for a general system near the ground state
with a ferromagnetic interaction and an opposing long range interaction. We
illustrate that the correlation functions associated with the exact dipolar
interactions differ substantially from those in which a scalar product form
between the dipoles is assumed.Comment: 17 pages, 9 figure
Explaining the Frequency of Alcohol Consumption in a Conflict Zone: Jews and Palestinians in Israel
Experiencing stress and exposure to terrorism may have an adverse effect on health risk behaviors. Few studies have examined alcohol use among adults living in Israel under chronic, stressful terrorism-related conditions. In this study, we examined the relationships of demographics, past stressful events, and terrorism exposure to the frequency of alcohol use and the mediating roles of depressive and post-traumatic stress disorder (PTSD) symptoms. We used three waves of data from a 2007–2008 nationally representative sample of Jewish and Palestinian adults in Israel. We assessed past stressful events, in addition to direct and indirect exposures to terrorism. Results indicated that past stressful events and exposure to terrorism were not directly associated with alcohol use, but were indirectly associated and mediated by depressive and PTSD symptomology. Mental health symptoms were differentially associated with alcohol use. More frequent drinking was mediated by higher levels of depression, including for women and Palestinians; however, PTSD symptom severity was related to less frequent drinking. Mental health may play a prominent role in the frequency of alcohol use among adults exposed to terrorism in Israel. Alcohol use, as a coping mechanism, may differ by demographic characteristics (gender and ethnicity) and psychological symptomology for adults living in a conflict zone in Israel
Demagnetization Borne Microscale Skyrmions
Magnetic systems are an exciting realm of study that is being explored on
smaller and smaller scales. One extremely interesting magnetic state that has
gained momentum in recent years is the skyrmionic state. It is characterized by
a vortex where the edge magnetic moments point opposite to the core. Although
skyrmions have many possible realizations, in practice, creating them in a lab
is a difficult task to accomplish. In this work, new methods for skyrmion
generation and customization are suggested. Skyrmionic behavior was numerically
observed in minimally customized simulations of spheres, hemisphere,
ellipsoids, and hemi-ellipsoids, for typ- ical Cobalt parameters, in a range
from approximately 40 nm to 120 nm in diameter simply by applying a field
Voltage dependence of Landau-Lifshitz-Gilbert damping of a spin in a current driven tunnel junction
We present a theory of Landau-Lifshitz-Gilbert damping for a
localized spin in the junction coupled to the conduction electrons
in both leads under an applied volatege . We find the voltage dependence of
the damping term reflecting the energy dependence of the density of states. We
find the effect is linear in the voltage and cotrolled by particle-hole
asymmetry of the leads.Comment: 6 pages, 3 figure
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