6,887 research outputs found
Myriad phases of the Checkerboard Hubbard Model
The zero temperature phase diagram of the checkerboard Hubbard model is
obtained in the solvable limit in which it consists of weakly coupled square
plaquettes. As a function of the on-site Coulomb repulsion U and the density of
holes per site, x, we demonstrate the existence of at least 16 distinct phases.
For instance, at zero doping, the ground state is a novel d-wave Mott insulator
(d-Mott), which is not adiabatically continuable to a band insulator; by doping
the d-Mott state with holes, depending on the magnitude of U, it gives way to a
d-wave superconducting state, a two-flavor spin-1/2 Fermi liquid (FL), or a
spin-3/2 FL.Comment: 4 pages, 2 figures, minor revisions, published in Phys. Rev. B as a
Rapid Communicatio
Superconducting proximity effect to the block antiferromagnetism in KFeSe
Recent discovery of superconducting (SC) ternary iron selenides has block
antiferromagentic (AFM) long range order. Many experiments show possible
mesoscopic phase separation of the superconductivity and antiferromagnetism,
while the neutron experiment reveals a sizable suppression of magnetic moment
due to the superconductivity indicating a possible phase coexistence. Here we
propose that the observed suppression of the magnetic moment may be explained
due to the proximity effect within a phase separation scenario. We use a
two-orbital model to study the proximity effect on a layer of block AFM state
induced by neighboring SC layers via an interlayer tunneling mechanism. We
argue that the proximity effect in ternary Fe-selenides should be large because
of the large interlayer coupling and weak electron correlation. The result of
our mean field theory is compared with the neutron experiments
semi-quantitatively. The suppression of the magnetic moment due to the SC
proximity effect is found to be more pronounced in the d-wave superconductivity
and may be enhanced by the frustrated structure of the block AFM state.Comment: 6 pages, 6 figure
The Friedberg-Lee model at finite temperature and density
The Friedberg-Lee model is studied at finite temperature and density. By
using the finite temperature field theory, the effective potential of the
Friedberg-Lee model and the bag constant and have been
calculated at different temperatures and densities. It is shown that there is a
critical temperature when
and a critical chemical potential for fixing
the temperature at . We also calculate the soliton solutions
of the Friedberg-Lee model at finite temperature and density. It turns out that
when (or ), there is a bag constant (or
) and the soliton solutions are stable. However, when (or
) the bag constant (or ) and there is no soliton solution anymore, therefore, the
confinement of quarks disappears quickly.Comment: 12 pages, 11 figures; version accepted for publication in Phys. Rev.
2-(4-Bromophenyl)quinoxaline
In the title compound, C14H9BrN2, the benzene and quinoxaline rings are almost coplanar [r.m.s. deviation = 0.0285 (3) Å and dihedral angle = 2.1 (2)°]
Team Triple-Check at Factify 2: Parameter-Efficient Large Foundation Models with Feature Representations for Multi-Modal Fact Verification
Multi-modal fact verification has become an important but challenging issue
on social media due to the mismatch between the text and images in the
misinformation of news content, which has been addressed by considering
cross-modalities to identify the veracity of the news in recent years. In this
paper, we propose the Pre-CoFactv2 framework with new parameter-efficient
foundation models for modeling fine-grained text and input embeddings with
lightening parameters, multi-modal multi-type fusion for not only capturing
relations for the same and different modalities but also for different types
(i.e., claim and document), and feature representations for explicitly
providing metadata for each sample. In addition, we introduce a unified
ensemble method to boost model performance by adjusting the importance of each
trained model with not only the weights but also the powers. Extensive
experiments show that Pre-CoFactv2 outperforms Pre-CoFact by a large margin and
achieved new state-of-the-art results at the Factify challenge at AAAI 2023. We
further illustrate model variations to verify the relative contributions of
different components. Our team won the first prize (F1-score: 81.82%) and we
made our code publicly available at
https://github.com/wwweiwei/Pre-CoFactv2-AAAI-2023.Comment: AAAI-23 DeFactify 2 Workshop (1st Prize
Theory for charge and orbital density-wave states in manganite LaSrMnO
We investigate the high temperature phase of layered manganites, and
demonstrate that the charge-orbital phase transition without magnetic order in
LaSrMnO can be understood in terms of the density wave
instability. The orbital ordering is found to be induced by the nesting between
segments of Fermi surface with different orbital characters. The simultaneous
charge and orbital orderings are elaborated with a mean field theory. The
ordered orbitals are shown to be .Comment: published versio
The Optimal Inhomogeneity for Superconductivity: Finite Size Studies
We report the results of exact diagonalization studies of Hubbard models on a
square lattice with periodic boundary conditions and various
degrees and patterns of inhomogeneity, which are represented by inequivalent
hopping integrals and . We focus primarily on two patterns, the
checkerboard and the striped cases, for a large range of values of the on-site
repulsion and doped hole concentration, . We present evidence that
superconductivity is strongest for of order the bandwidth, and intermediate
inhomogeneity, . The maximum value of the ``pair-binding
energy'' we have found with purely repulsive interactions is for the checkerboard Hubbard model with and .
Moreover, for near optimal values, our results are insensitive to changes in
boundary conditions, suggesting that the correlation length is sufficiently
short that finite size effects are already unimportant.Comment: 8 pages, 9 figures; minor revisions; more references adde
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