440 research outputs found
Mott insulating phases and quantum phase transitions of interacting spin-3/2 fermionic cold atoms in optical lattices at half filling
We study various Mott insulating phases of interacting spin-3/2 fermionic
ultracold atoms in two-dimensional square optical lattices at half filling.
Using a generalized one-band Hubbard model with hidden SO(5) symmetry, we
identify two distinct symmetry breaking phases: the degenerate
antiferromagnetic spin-dipole/spin-octupole ordering and spin-quadrupole
ordering, depending on the sign of the spin-dependent interaction. These two
competing orders exhibit very different symmetry properties, low energy
excitations and topological characterizations. Near the SU(4) symmetric point,
a quantum critical state with a -flux phase may emerge due to strong
quantum fluctuations, leading to spin algebraic correlations and gapless
excitations.Comment: 11 pages, 4 figure
Cross-linked CoMoO4/rGO nanosheets as oxygen reduction catalyst
Development of inexpensive and robust electrocatalysts towards oxygen reduction reaction
(ORR) is crucial for the cost-affordable manufacturing of metal-air batteries and fuel cells. Here
we show that cross-linked CoMoO4 nanosheets and reduced graphene oxide (CoMoO4/rGO) can
be integrated in a hybrid material under one-pot hydrothermal conditions, yielding a composite
material with promising catalytic activity for oxygen reduction reaction (ORR). Cyclic voltammetry
(CV) and linear sweep voltammetry (LSV) were used to investigate the efficiency of the fabricated
CoMoO4/rGO catalyst towards ORR in alkaline conditions. The CoMoO4/rGO composite revealed
the main reduction peak and onset potential centered at 0.78 and 0.89 V (vs. RHE), respectively.
This study shows that the CoMoO4/rGO composite is a highly promising catalyst for the ORR under
alkaline conditions, and potential noble metal replacement cathode in fuel cells and metal-air batteries
Inhomogeneous chiral symmetry breaking in noncommutative four fermion interactions
The generalization of the Gross-Neveu model for noncommutative 3+1 space-time
has been analyzed. We find indications that the chiral symmetry breaking occurs
for an inhomogeneous background as in the LOFF phase in condensed matter.Comment: 17 pages, 2 figures, published version, minor correction
Comments on Noncommutative Open String Theory: V-duality and Holography
In this paper we study the interplay of electric and magnetic backgrounds in
determining the decoupling limit of coincident D-branes towards a
noncommutative Yang-Mills (NCYM) or open string (NCOS) theory. No decoupling
limit has been found for NCYM with space-time noncommutativity. It is suggested
that there is a new duality, which we call V-duality, which acts on NCOS with
both space-space and space-time noncommutativity, resulting from decoupling in
Lorentz-boost related backgrounds. We also show that the holographic
correspondence, previously suggested by Li and Wu, between NCYM and its
supergravity dual can be generalized to NCOS as well.Comment: 23 pages, RevTex, typos corrected,PRD final versio
Nonuniform symmetry breaking in noncommutative theory
The spontaneous symmetry breaking in noncommutative theory
has been analyzed by using the formalism of the effective action for composite
operators in the Hartree-Fock approximation. It turns out that there is no
phase transition to a constant vacuum expectation of the field and the broken
phase corresponds to a nonuniform background. By considering the generated mass gap depends on the angles among
the momenta and and the noncommutativity parameter
. The order of the transition is not easily determinable in our
approximation.Comment: 18 pages, 4 figures, added reference
Discovery of Lorentz-violating Weyl fermion semimetal state in LaAlGe materials
We report theoretical and experimental discovery of Lorentz-violating Weyl
fermion semimetal type-II state in the LaAlGe class of materials. Previously
type-II Weyl state was predicted in WTe2 materials which remains unrealized in
surface experiments. We show theoretically and experimentally that LaAlGe class
of materials are the robust platforms for the study of type-II Weyl physics.Comment: This paper reports theoretical prediction and experimental discovery
together. A detailed theoretical paper describing the topology of the full
family of X(Lanthanides)AlGe materials will follow. Other related papers can
be found at http://physics.princeton.edu/zahidhasangroup/index_WS.htm
An annular gap acceleration model for -ray emission of pulsars
If the binding energy of the pulsar's surface is not so high (the case of a
neutron star), both the negative and positive charges will flow out freely from
the surface of the star. The annular free flow model for -ray emission
of pulsars is suggested in this paper. It is emphasized that: (1). Two kinds of
acceleration regions (annular and core) need to be taken into account. The
annular acceleration region is defined by the magnetic field lines that cross
the null charge surface within the light cylinder. (2). If the potential drop
in the annular region of a pulsar is high enough (normally the cases of young
pulsars), charges in both the annular and the core regions could be accelerated
and produce primary gamma-rays. Secondary pairs are generated in both regions
and stream outwards to power the broadband radiations. (3). The potential drop
in the annular region grows more rapidly than that in the core region. The
annular acceleration process is a key point to produce wide emission beams as
observed. (4). The advantages of both the polar cap and outer gap models are
retained in this model. The geometric properties of the -ray emission
from the annular flow is analogous to that presented in a previous work by Qiao
et al., which match the observations well. (5). Since charges with different
signs leave the pulsar through the annular and the core regions, respectively,
the current closure problem can be partially solved.Comment: 11 pages 2 figures, accepted by Chinese Journal of Astronomy and
Astrophysic
Determinants of genetic structure in a highly heterogeneous landscape in southwest China
Intra-specific genetic diversity is a fundamental component of biodiversity, and is key to species adaptation and persistence. However, significant knowledge gaps still exist in our understanding of the patterns of genetic diversity and their key determinants. Most previous investigations mainly utilized single-species and/or a limited number of explanatory variables; so here we mapped the patterns of plastid genetic diversity within 15 plant species, and explored the key determinants shaping these patterns using a wide range of variables. Population-level cpDNA sequence data for 15 plant species from the Longitudinal Range Gorge Region (LRGR), southwest China, were retrieved from literature and used to estimate haplotype diversity (H(D)) and population pairwise genetic differentiation (F(ST)) indices. Genetic diversity and divergence landscape surfaces were then generated based on the H(D) and F(ST), respectively, to clarify the patterns of genetic structure in the region. Subsequently, we analyzed the relationships between plastid genetic diversity and 16 explanatory variables (classified as anthropogenic, climatic, and topographic). We found that the highest genetic diversity occurred in the Yulong Mountain region, with a significant proportion (~74.81%) of the high diversity land area being located outside of protected areas. The highest genetic divergence was observed approximately along the 25°N latitudinal line, with notable peaks in the western and eastern edges of the LRGR. Genetic diversity (H(D)) was weakly but significantly positively correlated with both Latitude (lat) and Annual Mean Wet Day Frequency (wet), yet significantly negatively correlated with all of Longitude (long), Annual Mean Cloud Cover Percent (cld), Annual Mean Anthropogenic Flux (ahf), and Human Footprint Index (hfp). A combination of climatic, topographic, and anthropogenic factors explained a significant proportion (78%) of genetic variation, with topographic factors (lat and long) being the best predictors. Our analysis identified areas of high genetic diversity (genetic diversity âhotspotsâ) and divergence in the region, and these should be prioritized for conservation. This study contributes to a better understanding of the features that shape the distribution of plastid genetic diversity in the LRGR and thus would inform conservation management efforts in this species-rich, but vulnerable region
Bosonization and phase Diagram of the one-dimensional t-J model
We present an analytic study of the phase diagram of the one-dimensional t-J
model and a couple of its cousins. To deal with the interactions induced by the
no double occupancy constraints, we introduce a deformation of the Hubbard
operators. When the deformation parameter is small, the induced
interactions are softened, accessible by perturbation theory. We combine
bososnization with renormalization group techniques to map out the phase
diagram of the system. We argue that when , there is no essential
change in the phase diagram. Comparison with the existing results in the
literature obtained by other methods justifies our deformation approach.Comment: 24 pages, 1 Figur
Effective Potential and Spontaneous Symmetry Breaking in the Noncommutative phi^6 Model
We study the conditions for spontaneous symmetry breaking of the
(2+1)-dimensional noncommutative phi^6 model in the small-theta limit. In this
regime, considering the model as a cutoff theory, it is reasonable to assume
translational invariance as a property of the vacuum state and study the
conditions for spontaneous symmetry breaking by an effective potential
analysis. An investigation of up to the two loop level reveals that
noncommutative effects can modify drastically the shape of the effective
potential. Under reasonable conditions, the nonplanar sector of the theory can
become dominant and induce symmetry breaking for values of the mass and
coupling constants not reached by the commutative counterpart.Comment: 11 pages, 2 figures, corrected to match with the PRD versio
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