4,005 research outputs found
Numerical Study of Quantum Hall Bilayers at Total Filling : A New Phase at Intermediate Layer Distances
We study the phase diagram of quantum Hall bilayer systems with total filing
of the lowest Landau level as a function of layer distances
. Based on numerical exact diagonalization calculations, we obtain three
distinct phases, including an exciton superfluid phase with spontaneous
interlayer coherence at small , a composite Fermi liquid at large , and
an intermediate phase for ( is the magnetic length). The
transition from the exciton superfluid to the intermediate phase is identified
by (i) a dramatic change in the Berry curvature of the ground state under
twisted boundary conditions on the two layers; (ii) an energy level crossing of
the first excited state. The transition from the intermediate phase to the
composite Fermi liquid is identified by the vanishing of the exciton superfluid
stiffness. Furthermore, from our finite-size study, the energy cost of
transferring one electron between the layers shows an even-odd effect and
possibly extrapolates to a finite value in the thermodynamic limit, indicating
the enhanced intralayer correlation. Our identification of an intermediate
phase and its distinctive features shed new light on the theoretical
understanding of the quantum Hall bilayer system at total filling .Comment: 5 pages, 3 figures (main text); 5 pages, 4 figures (supplementary
material); to be published in PR
Robust non-Abelian spin liquid and possible intermediate phase in antiferromagnetic Kitaev model with magnetic field
We investigate the non-Abelian topological chiral spin liquid phase in the
two-dimensional (2D) Kitaev honeycomb model subject to a magnetic field. By
combining density matrix renormalization group (DMRG) and exact diagonalization
(ED) we study the energy spectra, entanglement, topological degeneracy, and
expectation values of Wilson loop operators, allowing for robust
characterization. While the ferromagnetic (FM) Kitaev spin liquid is already
destroyed by a weak magnetic field with Zeeman energy , the antiferromagnetic (AFM) spin liquid remains robust up to a magnetic
field that is an order of magnitude larger, .
Interestingly, for larger fields , an
intermediate gapless phase is observed, before a second transition to the
high-field partially-polarized paramagnet. We attribute this rich phase
diagram, and the remarkable stability of the chiral topological phase in the
AFM Kitaev model, to the interplay of strong spin-orbit coupling and
frustration enhanced by the magnetic field. Our findings suggest relevance to
recent experiments on RuCl under magnetic fields.Comment: 8 pages, 8 figure
Spin-Orbital Density Wave and a Mott Insulator in a Two-Orbital Hubbard Model on a Honeycomb Lattice
Inspired by recent discovery of correlated insulating states in twisted
bilayer graphene (TBG), we study a two-orbital Hubbard model on the honeycomb
lattice with two electrons per unit cell. Based on the real-space density
matrix renormalization group (DMRG) simulation, we identify a metal-insulator
transition around . In the vicinity of , we find strong
spin/orbital density wave fluctuations at commensurate wavevectors, accompanied
by weaker incommensurate charge density wave (CDW) fluctuations. The
spin/orbital density wave fluctuations are enhanced with increasing system
sizes, suggesting the possible emergence of long-range order in the two
dimensional limit. At larger , our calculations indicate a possible
nonmagnetic Mott insulator phase without spin or orbital polarization. Our
findings offer new insights into correlated electron phenomena in twisted
bilayer graphene and other multi-orbital honeycomb materials.Comment: 6 pages, 6 figure
Hyper-Activated Pro-Inflammatory CD16+ Monocytes Correlate with the Severity of Liver Injury and Fibrosis in Patients with Chronic Hepatitis B
BACKGROUND: Extensive mononuclear cell infiltration is strongly correlated with liver damage in patients with chronic hepatitis B virus (CHB) infection. Macrophages and infiltrating monocytes also participate in the development of liver damage and fibrosis in animal models. However, little is known regarding the immunopathogenic role of peripheral blood monocytes and intrahepatic macrophages. METHODOLOGY/PRINCIPAL FINDINGS: The frequencies, phenotypes, and functions of peripheral blood and intrahepatic monocyte/macrophage subsets were analyzed in 110 HBeAg positive CHB patients, including 32 immune tolerant (IT) carriers and 78 immune activated (IA) patients. Liver biopsies from 20 IA patients undergoing diagnosis were collected for immunohistochemical analysis. IA patients displayed significant increases in peripheral blood monocytes and intrahepatic macrophages as well as CD16(+) subsets, which were closely associated with serum alanine aminotransferase (ALT) levels and the liver histological activity index (HAI) scores. In addition, the increased CD16(+) monocytes/macrophages expressed higher levels of the activation marker HLA-DR compared with CD16(-) monocytes/macrophages. Furthermore, peripheral blood CD16(+) monocytes preferentially released inflammatory cytokines and hold higher potency in inducing the expansion of Th17 cells. Of note, hepatic neutrophils also positively correlated with HAI scores. CONCLUSIONS: These distinct properties of monocyte/macrophage subpopulations participate in fostering the inflammatory microenvironment and liver damage in CHB patients and further represent a collaborative scenario among different cell types contributing to the pathogenesis of HBV-induced liver disease
Valley Stoner Instability of the Composite Fermi Sea
We study two-component electrons in the lowest Landau level at total filling
factor with anisotropic mass tensors and principal axes rotated by
as realized in Aluminum Arsenide (AlAs) quantum wells. Combining exact
diagonalization and the density matrix renormalization group we demonstrate
that the system undergoes a quantum phase transition from a gapless state in
which both flavors are equally populated to another gapless state in which all
the electrons spontaneously polarize into a single flavor beyond a critical
mass anisotropy of {\bf }. We propose that this phase
transition is a form of itinerant Stoner transition between a two-component and
a single-component composite fermi sea states and describe a set of trial
wavefunctions which successfully capture the quantum numbers and shell filling
effects in finite size systems as well as providing a physical picture for the
energetics of these states. Our estimates indicate that the composite Fermi sea
of AlAs is the analog of an itinerant Stoner magnet with a finite spontaneous
valley polarization. We pinpoint experimental evidence indicating the presence
of Stoner magnetism in the Jain states surrounding .Comment: 7 pages, 4 figure
Broad bandwidth waveguide polarizer via grating mediated mode conversion
A polarization beam splitter (PBS) based on a four-layer slab waveguide is proposed, where a sub-wavelength grating is embedded between the waveguide core and the cladding. This grating not only affords Bragg momentum to tune the propagation constant of guiding modes but also converts the forward zero-order waveguide mode to the backward first one for a specific polarization. Thus, the incident light with polarization that satisfies the phase-matching condition is highly reflected in the waveguide, while other light with orthogonal polarization keeps intact and passes through it efficiently. Numerical simulations show that one can make the compact PBS for both polarizations with an extinction ratio higher than 35 dB, a waveband larger than 80 nm, a grating period tolerance of 20 nm, and a waveguide height tolerance of 80 nm. The revealed mode conversion mechanism via the sub-wavelength grating enriches the design of PBSs for integrated silicon waveguide chips
Anisotropy-driven transition from the Moore-Read state to quantum Hall stripes
We investigate the nature of the quantum Hall liquid in a half-filled second Landau level (n=1) as a function of band mass anisotropy using numerical exact diagonalization and density matrix renormalization group methods. We find increasing the mass anisotropy induces a quantum phase transition from the Moore-Read state to a charge density wave state. By analyzing the energy spectrum, guiding center structure factors, and by adding weak pinning potentials, we show that this charge density wave is a unidirectional quantum Hall stripe, which has a periodicity of a few magnetic lengths and survives in the thermodynamic limit. We find smooth profiles for the guiding center occupation function that reveal the strong coupling nature of the array of chiral Luttinger liquids residing at the stripe edges
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