599 research outputs found
Supersolidity and phase diagram of softcore bosons in a triangular lattice
We study the softcore extended Bose Hubbard model in a two-dimensional
triangular lattice by using the quantum Monte Carlo methods. The ground state
phase diagram of the system exhibits a very fruitful structure. Except the Mott
insulating state, four kinds of solid states with respect to the commensurate
filling factors and are identified. Two of them (CDW II
and CDW III) are newly predicted. In incommensurate fillings, superfluid,
spuersolid as well as phase separation states are detected . As in the case for
the hardcore bosons, a supersolid phase exists in while it is
unstable towards the phase separation in . However, this instability
is refrained in due to the softening of the bosons and then a
supersolid phase survives.Comment: 4 pages, 5 figure
Quantum Renormalization of the Spin Hall Effect
By quantum Monte Carlo simulation of a realistic multiorbital Anderson
impurity model, we study the spin-orbit interaction (SOI) of an Fe impurity in
Au host metal. We show, for the first time, that the SOI is strongly
renormalized by the quantum spin fluctuation. Based on this mechanism, we can
explain why the gigantic spin Hall effect in Au with Fe impurities was observed
in recent experiment, while it is not visible in the anomalous Hall effect. In
addition, we show that the SOI is strongly renormalized by the Coulomb
correlation U. Based on this picture, we can explain past discrepancies in the
calculated orbital angular momenta for an Fe impurity in an Au host.Comment: 4 pages, 3 figure
Unconventional Superconducting Symmetry in a Checkerboard Antiferromagnet
We use a renormalized mean field theory to study the Gutzwiller projected BCS
states of the extended Hubbard model in the large limit, or the
--- model on a two-dimensional checkerboard lattice. At small
, the frustration due to the diagonal terms of and does not
alter the -wave pairing symmetry, and the negative (positive)
enhances (suppresses) the pairing order parameter. At large , the
ground state has an extended s-wave symmetry. At the intermediate , the
ground state is or -wave with time reversal symmetry broken.Comment: 6 pages, 6 figure
The Extended Bose Hubbard Model on the Two Dimensional Honeycomb Lattice
We study the extended Bose-Hubbard model on a two-dimensional honeycomb
lattice by using large scale quantum Monte Carlo simulations. We present the
ground state phase diagrams for both the hard-core case and the soft-core case.
For the hard-core case, the transition between solid and the
superfluid is first order and the supersolid state is unstable towards phase
separation. For the soft-core case, due to the presence of the multiple
occupation, a stable particle induced supersolid (SS-p) phase emerges when
. The transition from the solid at to the SS-p is second
order with the superfluid density scaling as . The
SS-p has the same diagonal order as the solid at . As the chemical
potential increasing further, the SS-p will turn into a solid where two bosons
occupying each site of a sublattice through a first order transition. We also
calculate the critical exponents of the transition between solid and
superfluid at the Heisenberg point for the hard core case. We find the
dynamical critical exponent , which is smaller than results obtained on
smaller lattices. This indicates that approaches zero in the
thermodynamic limit, so the transition is also first order even at the
Heisenberg point.Comment: 6pages, 6figure
Cross-thought for sentence encoder pre-training
In this paper, we propose Cross-Thought, a novel approach to pre-training
sequence encoder, which is instrumental in building reusable sequence
embeddings for large-scale NLP tasks such as question answering. Instead of
using the original signals of full sentences, we train a Transformer-based
sequence encoder over a large set of short sequences, which allows the model to
automatically select the most useful information for predicting masked words.
Experiments on question answering and textual entailment tasks demonstrate that
our pre-trained encoder can outperform state-of-the-art encoders trained with
continuous sentence signals as well as traditional masked language modeling
baselines. Our proposed approach also achieves new state of the art on HotpotQA
(full-wiki setting) by improving intermediate information retrieval
performance.Comment: Accepted by EMNLP 202
Energy Chaos Characteristic Evolution Analysis of Sandstones during Multilevel Unloading Subject to Different Confining Pressures
AbstractIn this study, multilevel and conventional unloading triaxial compression tests under different confining pressures are separately carried out to systematically reveal the deformation, energy evolution, and fracture characteristics of sandstone samples. Results show that under the multilevel unloading condition, the increase of the initial confining pressure has a more obvious inhibitory effect on the radial strain of sandstone, and the samples can fully exhibit elastic deformation and partial plastic deformation, showing obvious plastic characteristics. The radial energy growth factor is more sensitive than the axial energy growth factor during the process of confining pressure unloading, and the larger the initial confining pressure, the earlier the period-doubling bifurcation region and chaotic region are reached. To better understand the deformation and failure process of rock during engineering excavation, it is necessary to establish a constitutive relation describing the mechanical properties of rock. The three-step failure mode also proves that there are tensile and shear fractures in sandstone samples, in which the effects of tensile stress and shear stress are more or less interdependent in the failure process. It can be seen that multilevel unloading makes the energy conversion more adequate and reduces the sudden release of energy when the rock fails, reducing the possibility of rockburst and making the excavation unloading process safer. This will deepen the understanding of rock failure behavior and contribute to the better application of energy characteristics to relevant engineering practices
Dependence of Chemical Abundance on the Cosmic Ray Ionization Rate in IC 348
Ions (e.g., H, HO) have been used extensively to quantify the
cosmic-ray ionization rate (CRIR) in diffuse sightlines. However, measurements
of CRIR in low-to-intermediate density gas environments are rare, especially
when background stars are absent. In this work, we combine molecular line
observations of CO, OH, CH, and HCO in the star-forming cloud IC~348, and
chemical models to constrain the value of CRIR and study the response of the
chemical abundances distribution. The cloud boundary is found to have an
of approximately 4 mag. From the interior to the exterior of the
cloud, the observed CO line intensities drop by an order of magnitude.
The calculated average abundance of CO (assuming C/C = 65)
is (1.20.9) 10, which increases by a factor of 6 from the
interior to the outside regions. The average abundance of CH (3.30.7
10) is in good agreement with previous findings in diffuse and
translucent clouds ( 5 mag). However, we did not find a decline
in CH abundance in regions of high extinction (8 mag) as
previously reported in Taurus. By comparing the observed molecular abundances
and chemical models, we find a decreasing trend of CRIR as
increases. The inferred CRIR of = (4.71.5)
10 s at low is consistent with H measurements
toward two nearby massive stars.Comment: 21 pages, 11 figures. Submitted to Ap
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