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 $\pm 1$) 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