3,468 research outputs found
Spin Ferroquadrupolar Order in the Nematic Phase of FeSe
We provide evidence that spin ferroquadrupolar (FQ) order is the likely
ground state in the nonmagnetic nematic phase of stoichiometric FeSe. By
studying the variational mean-field phase diagram of a bilinear-biquadratic
Heisenberg model up to the 2nd nearest neighbor, we find the FQ phase in close
proximity to the columnar antiferromagnet commonly realized in iron-based
superconductors; the stability of FQ phase is further verified by the density
matrix renormalization group. The dynamical spin structure factor in the FQ
state is calculated with flavor-wave theory, which yields a qualitatively
consistent result with inelastic neutron scattering experiments on FeSe at both
low and high energies. We verify that FQ can coexist with breaking
environments in the mean-field calculation, and further discuss the possibility
that quantum fluctuations in FQ act as a source of nematicity.Comment: 8 pages, 7 figures, Erratum adde
Unified Spin Model for Magnetic Excitations in Iron Chalcogenides
Recent inelastic neutron scattering (INS) measurements on FeSe and
Fe(TeSe), have sparked intense debate over the nature of the ground
state in these materials. Here we propose an effective bilinear-biquadratic
spin model which is shown to consistently describe the evolution of low-energy
spin excitations in FeSe, both under applied pressure and upon Se/Te
substitution. The phase diagram, studied using a combination of variational
mean-field, flavor-wave calculations, and density-matrix renormalization group
(DMRG), exhibits a sequence of transitions between the columnar antiferromagnet
common to the iron pnictides, the non-magnetic ferroquadrupolar phase
attributed to FeSe, and the double-stripe antiferromagnetic order known to
exist in FeTe. The calculated spin structure factor in these phases
mimics closely that observed with INS in the Fe(TeSe), series. In
addition to the experimentally established phases, the possibility of
incommensurate magnetic order is also predicted.Comment: 9 pages, 10 figures in the main text; plus 5 pages of supplementary
material
Dynamical Mean Field Theory for the Bose-Hubbard Model
The dynamical mean field theory (DMFT), which is successful in the study of
strongly correlated fermions, was recently extended to boson systems [Phys.
Rev. B {\textbf 77}, 235106 (2008)]. In this paper, we employ the bosonic DMFT
to study the Bose-Hubbard model which describes on-site interacting bosons in a
lattice. Using exact diagonalization as the impurity solver, we get the DMFT
solutions for the Green's function, the occupation density, as well as the
condensate fraction on a Bethe lattice. Various phases are identified: the Mott
insulator, the Bose-Einstein condensed (BEC) phase, and the normal phase. At
finite temperatures, we obtain the crossover between the Mott-like regime and
the normal phase, as well as the BEC-to-normal phase transition. Phase diagrams
on the plane and on the plane are
produced ( is the scaled hopping amplitude). We compare our results
with the previous ones, and discuss the implication of these results to
experiments.Comment: 11 pages, 8 figure
DEFINITION AND CONSTRUCTION OF THE CORE COMPETENCE IN REAL ESTATE INDUSTRY
The real estate is a very high risk profession. Its funds devotion is big, the operation period is long and the market change quickly. At the same time, the real estate has to face the high level competition that brought by international capital investment. The key to deal with these problems is how to set up and enhance the core competence of the real estate industry while integrating the strategic resources. In this paper we will analyze the features of core competence, thus define the core competence in real estate Industry. The main competition factors of real estate industry include land resources, capital scale and market management. Accordingly, we put forward the solution to establish the core competence of real estate industry. Key words: Core competence, Real estate, Investmen
Spin liquid nature in the Heisenberg - triangular antiferromagnet
We investigate the spin- Heisenberg model on the triangular
lattice in the presence of nearest-neighbor and next-nearest-neighbor
antiferromagnetic couplings. Motivated by recent findings from
density-matrix renormalization group (DMRG) claiming the existence of a gapped
spin liquid with signatures of spontaneously broken lattice point group
symmetry [Zhu and White, Phys. Rev. B 92, 041105 (2015); Hu, Gong, Zhu, and
Sheng, Phys. Rev. B 92, 140403 (2015)], we employ the variational Monte Carlo
(VMC) approach to analyze the model from an alternative perspective that
considers both magnetically ordered and paramagnetic trial states. We find a
quantum paramagnet in the regime , framed by
coplanar (stripe collinear) antiferromagnetic order for smaller
(larger) . By considering the optimization of spin-liquid wave
functions of a different gauge group and lattice point group content as derived
from Abrikosov mean-field theory, we obtain the gapless Dirac spin
liquid as the energetically most preferable state in comparison to all
symmetric or nematic gapped spin liquids so far advocated by
DMRG. Moreover, by the application of few Lanczos iterations, we find the
energy to be the same as the DMRG result within error-bars. To further resolve
the intriguing disagreement between VMC and DMRG, we complement our
methodological approach by the pseudofermion functional renormalization group
(PFFRG) to compare the spin structure factors for the paramagnetic regime
calculated by VMC, DMRG, and PFFRG. This model promises to be an ideal test-bed
for future numerical refinements in tracking the long-range correlations in
frustrated magnets.Comment: Editors' Suggestion. 16 pages, 13 figures, 4 table
Variational Monte Carlo study of gapless spin liquid in the spin- XXZ antiferromagnetic model on the kagome lattice
By using the variational Monte Carlo technique, we study the spin- XXZ
antiferromagnetic model (with easy-plane anisotropy) on the kagome lattice. A
class of Gutzwiller projected fermionic states with a spin Jastrow factor is
considered to describe either spin liquids (with or symmetry) or
magnetically ordered phases (with or ). We
find that the magnetic states are not stable in the thermodynamic limit.
Moreover, there is no energy gain to break the gauge symmetry from to
within the spin-liquid states, as previously found in the Heisenberg
model. The best variational wave function is therefore the Dirac state,
supplemented by the spin Jastrow factor. Furthermore, a vanishing spin
gap is obtained at the variational level, in the whole regime from the to
the Heisenberg model.Comment: 7 pages, 7 figure
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