7,385 research outputs found
Magnetic Susceptibility of the Kagome Antiferromagnet ZnCu3(OH)6Cl2
We analyze the experimental data for the magnetic susceptibility of the
material ZnCu3(OH)6Cl2 in terms of the Kagome Lattice Heisenberg model (KLHM),
discussing possible role of impurity spins, dilution, exchange anisotropy, and
both out-of-plane and in-plane Dzyaloshinsky-Moriya (DM) anisotropies, with
explicit theoretical calculations using the Numerical Linked Cluster (NLC)
method and exact diagonalization (ED). The high-temperature experimental data
are well described by the pure Heisenberg model with J=170 K. We show that the
sudden upturn in the susceptibility around T=75 K is due to DM interactions. We
also observe that at intermediate temperatures, below T=J, our calculated
susceptibility for KLHM fits well with a power law T^{-0.25}.Comment: 4 pages, 5 figures, published versio
Two-dimensional Lattice Gauge Theories with Superconducting Quantum Circuits
A quantum simulator of U(1) lattice gauge theories can be implemented with
superconducting circuits. This allows the investigation of confined and
deconfined phases in quantum link models, and of valence bond solid and spin
liquid phases in quantum dimer models. Fractionalized confining strings and the
real-time dynamics of quantum phase transitions are accessible as well. Here we
show how state-of-the-art superconducting technology allows us to simulate
these phenomena in relatively small circuit lattices. By exploiting the strong
non-linear couplings between quantized excitations emerging when
superconducting qubits are coupled, we show how to engineer gauge invariant
Hamiltonians, including ring-exchange and four-body Ising interactions. We
demonstrate that, despite decoherence and disorder effects, minimal circuit
instances allow us to investigate properties such as the dynamics of electric
flux strings, signaling confinement in gauge invariant field theories. The
experimental realization of these models in larger superconducting circuits
could address open questions beyond current computational capability.Comment: Published versio
Particle linear theory on a self-gravitating perturbed cubic Bravais lattice
Discreteness effects are a source of uncontrolled systematic errors of N-body
simulations, which are used to compute the evolution of a self-gravitating
fluid. We have already developed the so-called "Particle Linear Theory" (PLT),
which describes the evolution of the position of self-gravitating particles
located on a perturbed simple cubic lattice. It is the discrete analogue of the
well-known (Lagrangian) linear theory of a self-gravitating fluid. Comparing
both theories permits to quantify precisely discreteness effects in the linear
regime. It is useful to develop the PLT also for other perturbed lattices
because they represent different discretizations of the same continuous system.
In this paper we detail how to implement the PLT for perturbed cubic Bravais
lattices (simple, body and face-centered) in a cubic simulation box. As an
application, we will study the discreteness effects -- in the linear regime --
of N-body simulations for which initial conditions have been set-up using these
different lattices.Comment: 9 pages, 4 figures and 4 tables. Minor corrections to match published
versio
Disorder is not always bad for charge-to-spin conversion in WTe2
The Wang group at Stanford University demonstrates disordered WTex films for efficient charge-to-spin conversion phenomena. The deposition of these films by sputtering and the charge-to-spin conversion resilience against disorder make them attractive for applications in new magnetic memory devices
Breathing mode for systems of interacting particles
We study the breathing mode in systems of trapped interacting particles. Our
approach, based on a dynamical ansatz in the first equation of the
Bogolyubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy allows us to tackle at
once a wide range of power law interactions and interaction strengths, at
linear and non linear levels. This both puts in a common framework various
results scattered in the literature, and by widely generalizing these,
emphasizes universal characters of this breathing mode. Our findings are
supported by direct numerical simulations.Comment: 4 pages, 4 figure
Experimentally realizable quantum comparison of coherent states and its applications
When comparing quantum states to each other, it is possible to obtain an
unambiguous answer, indicating that the states are definitely different,
already after a single measurement. In this paper we investigate comparison of
coherent states, which is the simplest example of quantum state comparison for
continuous variables. The method we present has a high success probability, and
is experimentally feasible to realize as the only required components are beam
splitters and photon detectors. An easily realizable method for quantum state
comparison could be important for real applications. As examples of such
applications we present a "lock and key" scheme and a simple scheme for quantum
public key distribution.Comment: 14 pages, 5 figures, version one submitted to PRA. Version two is the
final accepted versio
Spatio-temporal variability of the North Sea cod recruitment in relation to temperature and zooplankton
The North Sea cod (Gadus morhua, L.) stock has continuously declined over the past four decades linked with overfishing
and climate change. Changes in stock structure due to overfishing have made the stock largely dependent on its
recruitment success, which greatly relies on environmental conditions. Here we focus on the spatio-temporal variability of
cod recruitment in an effort to detect changes during the critical early life stages. Using International Bottom Trawl Survey
(IBTS) data from 1974 to 2011, a major spatio-temporal change in the distribution of cod recruits was identified in the late
1990s, characterized by a pronounced decrease in the central and southeastern North Sea stock. Other minor spatial
changes were also recorded in the mid-1980s and early 1990s. We tested whether the observed changes in recruits
distribution could be related with direct (i.e. temperature) and/or indirect (i.e. changes in the quantity and quality of
zooplankton prey) effects of climate variability. The analyses were based on spatially-resolved time series, i.e. sea surface
temperature (SST) from the Hadley Center and zooplankton records from the Continuous Plankton Recorder Survey. We
showed that spring SST increase was the main driver for the most recent decrease in cod recruitment. The late 1990s were
also characterized by relatively low total zooplankton biomass, particularly of energy-rich zooplankton such as the copepod
Calanus finmarchicus
, which have further contributed to the decline of North Sea cod recruitment. Long-term spatially-
resolved observations were used to produce regional distribution models that could further be used to predict the
abundance of North Sea cod recruits based on temperature and zooplankton food availability.Publicado
- …