3,360 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
Topological phases protected by point group symmetry
We consider symmetry protected topological (SPT) phases with crystalline
point group symmetry, dubbed point group SPT (pgSPT) phases. We show that such
phases can be understood in terms of lower-dimensional topological phases with
on-site symmetry, and can be constructed as stacks and arrays of these
lower-dimensional states. This provides the basis for a general framework to
classify and characterize bosonic and fermionic pgSPT phases, that can be
applied for arbitrary crystalline point group symmetry and in arbitrary spatial
dimension. We develop and illustrate this framework by means of a few examples,
focusing on three-dimensional states. We classify bosonic pgSPT phases and
fermionic topological crystalline superconductors with (reflection)
symmetry, electronic topological crystalline insulators (TCIs) with symmetry, and bosonic pgSPT phases with symmetry,
which is generated by two perpendicular mirror reflections. We also study
surface properties, with a focus on gapped, topologically ordered surface
states. For electronic TCIs we find a classification, where
the corresponds to known states obtained from non-interacting electrons,
and the corresponds to a "strongly correlated" TCI that requires strong
interactions in the bulk. Our approach may also point the way toward a general
theory of symmetry enriched topological (SET) phases with crystalline point
group symmetry.Comment: v2: Minor changes/additions to introduction and discussion sections,
references added, published version. 21 pages, 11 figure
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
Rapid Amygdala Kindling Causes Motor Seizure and Comorbidity of Anxiety- and Depression-Like Behaviors in Rats
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
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