5,340 research outputs found
An exact chiral spin liquid with non-Abelian anyons
We establish the existence of a chiral spin liquid (CSL) as the exact ground
state of the Kitaev model on a decorated honeycomb lattice, which is obtained
by replacing each site in the familiar honeycomb lattice with a triangle. The
CSL state spontaneously breaks time reversal symmetry but preserves other
symmetries. There are two topologically distinct CSLs separated by a quantum
critical point. Interestingly, vortex excitations in the topologically
nontrivial (Chern number ) CSL obey non-Abelian statistics.Comment: 4 pages, 2 figures; published version in Phys. Rev. Let
Fragile Mott Insulators
We prove that there exists a class of crystalline insulators, which we call
"fragile Mott insulators" which are not adiabatically connected to any sort of
band insulator provided time-reversal and certain point-group symmetries are
respected, but which are otherwise unspectacular in that they exhibit no
topological order nor any form of fractionalized quasiparticles. Different
fragile Mott insulators are characterized by different nontrivial
one-dimensional representations of the crystal point group. We illustrate this
new type of insulators with two examples: the d-Mott insulator discovered in
the checkerboard Hubbard model at half-filling and the
Affleck-Kennedy-Lieb-Tasaki insulator on the square lattice.Comment: 4 pages, 2 figures. Published version in PRL. The name "Weak Mott
Insulators" is changed to "Fragile Mott Insulators" to avoid confusing in
terminolog
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
Are There Managerial Practices Associated with Service Delivery Collaboration Success?: Evidence from British Crime and Disorder Reduction Partnerships
Little empirical work exists measuring if interagency collaborations delivering public services produce better outcomes, and none looking inside the black box at collaboration management practices. We examine whether there are collaboration management practices associated with improved performance of Crime and Disorder Reduction Partnerships, a crossagency collaboration in England and Wales. These exist in every local authority in England and Wales, so there are enough of them to permit quantitative analysis. And their aim is crime reduction, and crime data over time are available, allowing actual results (rather than perceptions or self-reports) to be analyzed longitudinally. We find that there are management practices associated with greater success at reducing crime, mostly exhibited through interaction effects such that the practice in question is effective in some circumstances but not others. Our findings support the arguments of those arguing that effective management of collaborations is associated with tools for managing any organization, not ones unique to managing collaborations: if you want to be a good collaboration manager, you should be a good manager, period.
Fermi-surface reconstruction in a smectic phase of a high temperature superconductor
It is shown that, in the presence of a moderately strong C_4 symmetry
breaking (which could be produced either by lattice orthorhombicity or the
presence of an electron nematic phase), a weak, period 4, unidirectional charge
density wave ("charge stripe") order can reconstruct the Fermi surface of a
typical hole-doped cuprate to produce a small electron pocket. This form of
charge density wave order is consistent with that adduced from recent high
field NMR experiments in YBCO. The Fermi pocket has an area and effective mass
which is a rough caricature of those seen in recent high field quantum
oscillation experiments.Comment: 4 pages, 2 figures, minor change
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