858 research outputs found
Non-linear quantum critical transport and the Schwinger Mechanism
Scaling arguments imply that quantum critical points exhibit universal
non-linear responses to external probes. We investigate the origins of such
non-linearities in transport, which is especially problematic since the system
is necessarily driven far from equilibrium. We argue that for a wide class of
systems the new ingredient that enters is the Schwinger mechanism--the
production of carriers from the vacuum by the applied field-- which is then
balanced against a scattering rate which is itself set by the field. We show by
explicit computation how this works for the case of the symmetric
superfluid-Mott insulator transition of bosons
Coulomb and Hard Core Skyrmion Tails
Quantum Hall skyrmions are quantized solitons of a ferromagnetic O(3)
sigma-model. The reference, classical, solutions depend upon the interaction
between the electrons and exhibit completely different asymptotic profiles for
the physical Coulomb interaction than for the model hard core interaction
frequently used to generate variational wavefunctions. In this note we show, by
means of numerical calculations on (large) finite size systems at nu=1, that
this physically important difference, crucial for a sharp definition of their
statistics, persists for the quantized skyrmions at n=1.Comment: Revtex 9 pages, figs.ps files at
ftp://landau.calstatela.edu/pub/tailfig
Health needs and co-morbidity among detainees in contact with healthcare professionals within police custody across the London Metropolitan Police Service area
Aims
Detainees requiring access to healthcare services in police custody have been shown to suffer from poor physical and mental health, often exacerbated by substance misuse. This study examines the extent and nature of health needs in police custody across the Metropolitan Police Service (MPS), London.
Methods
A survey (n = 1657) was administered by Healthcare Professionals (HCP) for one month in 2015 across all MPS custody suites representing a 73% response rate. A logistic regression model was created using four binary outcomes (whether a detainee was a drug user, had mental health issues including self-harm and had an alcohol use disorder) with ten prognostics to test for co-morbid associations. A multiple imputation method using chained equations was used to manage missing cases.
Findings
High rates of physical health conditions, drug use, problematic alcohol use were noted but are within the upper range of existing studies. Mental health, self-harm and overall substance misuse levels (illicit drug user and a current drinker) were shown to be higher than other published studies. The logistic regression model found statistically significant associations between drug use, alcohol consumption and mental health including self-harm. Age was also found to be a key confounding factor. Physical health was broadly negatively associated with the four main outcomes.
Discussion
Levels of need for health interventions among the detainee population in London are broadly consistent with other European centres. There is a need for police custody staff to consider detainees' dual diagnosis needs. The development of integrated interventions alongside the enhanced clinical management of alcohol, drug use and mental health was considered
Correlation function diagnostics for type-I fracton phases
Fracton phases are recent entrants to the roster of topological phases in
three dimensions. They are characterized by subextensively divergent
topological degeneracy and excitations that are constrained to move along lower
dimensional subspaces, including the eponymous fractons that are immobile in
isolation. We develop correlation function diagnostics to characterize Type I
fracton phases which build on their exhibiting {\it partial deconfinement}.
These are inspired by similar diagnostics from standard gauge theories and
utilize a generalized gauging procedure that links fracton phases to classical
Ising models with subsystem symmetries. En route, we explicitly construct the
spacetime partition function for the plaquette Ising model which, under such
gauging, maps into the X-cube fracton topological phase. We numerically verify
our results for this model via Monte Carlo calculations
Rare region effects dominate weakly disordered 3D Dirac points
We study three-dimensional Dirac fermions with weak finite-range scalar
potential disorder. In the clean system, the density of states vanishes
quadratically at the Dirac point. Disorder is known to be perturbatively
irrelevant, and previous theoretical work has assumed that the Dirac semimetal
phase, characterized by a vanishing density of states, survives at weak
disorder, with a finite disorder phase transition to a diffusive metal with a
non-vanishing density of states. In this paper we show that nonperturbative
effects from rare regions, which are missed by conventional disorder-averaged
calculations, instead give rise to a nonzero density of states for any nonzero
disorder. Thus, there is no Dirac semimetal phase at non-zero disorder. The
results are established both by a heuristic scaling argument and via a
systematic saddle point analysis. We also discuss transport near the Dirac
point. At the Dirac point, we argue that transport is diffusive, and proceeds
via hopping between rare resonances. As one moves in chemical potential away
from the Dirac point, there are interesting intermediate-energy regimes where
the rare regions produce scattering resonances that determine the DC
conductivity. We derive a scaling theory of transport near disordered 3D Dirac
points. We also discuss the interplay of disorder with attractive interactions
at the Dirac point, and the resulting granular superconducting and Bose glass
phases. Our results are relevant for all 3D systems with Dirac points,
including Weyl semimetals.Comment: Expanded version of 1307.3252 with many new results, including a new
section showing how the results may be derived using a systematic saddle
point calculatio
Quantum Hall Skyrmions with Higher Topological Charge
We have investigated quantum Hall skyrmions at filling factor \nu=1 carrying
more than one unit of topological, and hence electric, charge. Using a
combination of analytic and numerical methods we find the counterintuitive
result that when the Zeeman energy is tuned to values much smaller than the
interaction energy (g \mu_B B/(e^2/\epsilon\ell) < 9*10^{-5}),the creation
energy of a charge two skyrmion becomes less than twice the creation energy of
a charge one skyrmion, i.e. skyrmions bind in pairs. The doubly charged
skyrmions are stable to further accretion of charge and exhibit a 10% larger
spin per unit charge than charge one skyrmions which would, in principle,
signal this pairing.Comment: 4 pages, 3 figures. Submitted to Phys. Rev. B, Rapid Communication
Nature of the spin liquid state of the Hubbard model on honeycomb lattice
Recent numerical work (Nature 464, 847 (2010)) indicates the existence of a
spin liquid phase (SL) that intervenes between the antiferromagnetic and
semimetallic phases of the half filled Hubbard model on a honeycomb lattice. To
better understand the nature of this exotic phase, we study the quantum
spin model on the honeycomb lattice, which provides an effective
description of the Mott insulating region of the Hubbard model. Employing the
variational Monte Carlo approach, we analyze the phase diagram of the model,
finding a phase transition between antiferromagnet and an unusual SL
state at , which we identify as the SL phase of the
Hubbard model. At higher we find a transition to a
dimerized state with spontaneously broken rotational symmetry.Comment: 5 pages, 6 figure
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