15,538 research outputs found
Phase Diagram of the Hubbard Model: Beyond the Dynamical Mean Field
The Dynamical Cluster Approximation (DCA) is used to study non-local
corrections to the dynamical mean field phase diagram of the two-dimensional
Hubbard model. Regions of antiferromagnetic, d-wave superconducting,
pseudo-gapped non-Fermi liquid, and Fermi liquid behaviors are found, in rough
agreement with the generic phase diagram of the cuprates. The non-local
fluctuations beyond the mean field both suppress the antiferromagnetism and
mediate the superconductivity.Comment: 4 pages, 5 eps figures, submitted to PR
Superconductivity in striped and multi-Fermi-surface Hubbard models: From the cuprates to the pnictides
Single- and multi-band Hubbard models have been found to describe many of the
complex phenomena that are observed in the cuprate and iron-based
high-temperature superconductors. Simulations of these models therefore provide
an ideal framework to study and understand the superconducting properties of
these systems and the mechanisms responsible for them. Here we review recent
dynamic cluster quantum Monte Carlo simulations of these models, which provide
an unbiased view of the leading correlations in the system. In particular, we
discuss what these simulations tell us about superconductivity in the
homogeneous 2D single-orbital Hubbard model, and how charge stripes affect this
behavior. We then describe recent simulations of a bilayer Hubbard model, which
provides a simple model to study the type and nature of pairing in systems with
multiple Fermi surfaces such as the iron-based superconductors.Comment: Published as part of Superstripes 2011 (Rome) conference proceeding
Noise-Activated Escape from a Sloshing Potential Well
We treat the noise-activated escape from a one-dimensional potential well of
an overdamped particle, to which a periodic force of fixed frequency is
applied. We determine the boundary layer behavior, and the physically relevant
length scales, near the oscillating well top. We show how stochastic behavior
near the well top generalizes the behavior first determined by Kramers, in the
case without forcing. Both the case when the forcing dies away in the weak
noise limit, and the case when it does not, are examined. We also discuss the
relevance of various scaling regimes to recent optical trap experiments.Comment: 9 pages, no figures, REVTeX, expanded versio
Tunable graphene-based polarizer
It is shown that an attenuated total reflection structure containing a
graphene layer can operate as a tunable polarizer of the electromagnetic
radiation. The polarization angle is controlled by adjusting the voltage
applied to graphene via external gate. The mechanism is based on the resonant
coupling of polarized electromagnetic waves to the surface
plasmon-polaritons in graphene. The presented calculations show that, at
resonance, the reflected wave is almost 100% polarized.Comment: submitted to the Applied Physics Letter
Rotating system for four-dimensional transverse rms-emittance measurements
Knowledge of the transverse four-dimensional beam rms-parameters is essential
for applications that involve lattice elements that couple the two transverse
degrees of freedom (planes). Of special interest is the removal of inter-plane
correlations to reduce the projected emittances. A dedicated ROtating System
for Emittance measurements (ROSE) has been proposed, developed, and
successfully commissioned to fully determine the four-dimensional beam matrix.
This device has been used at the High Charge injector (HLI) at GSI using a beam
line which is composed of a skew quadrupole triplet, a normal quadrupole
doublet, and ROSE. Mathematical algorithms, measurements, and results for ion
beams of 83Kr13+ at 1.4 MeV/u are reported in this paper.Comment: 11 pages, 10 figure
Buffering plasmons in nanoparticle waveguides at the virtual-localized transition
We study the plasmonic energy transfer from a locally excited nanoparticle
(LE-NP) to a linear array of small NPs and we obtain the parametric dependence
of the response function. An analytical expression allows us to distinguish the
extended resonant states and the localized ones, as well as an elusive regime
of virtual states. This last appears when the resonance width collapses and
before it becomes a localized state. Contrary to common wisdom, the highest
excitation transfer does not occur when the system has a well defined extended
resonant state but just at the virtual-localized transition, where the main
plasmonic modes have eigenfrequencies at the passband edge. The slow group
velocity at this critical frequency enables the excitation buffering and hence
favors a strong signal inside the chain. A similar situation should appear in
many other physical systems. The extreme sensitivity of this transition to the
waveguide and LE-NP parameters provides new tools for plasmonics.Comment: Regular article: 7 pages and 5 figure
Probably Safe or Live
This paper presents a formal characterisation of safety and liveness
properties \`a la Alpern and Schneider for fully probabilistic systems. As for
the classical setting, it is established that any (probabilistic tree) property
is equivalent to a conjunction of a safety and liveness property. A simple
algorithm is provided to obtain such property decomposition for flat
probabilistic CTL (PCTL). A safe fragment of PCTL is identified that provides a
sound and complete characterisation of safety properties. For liveness
properties, we provide two PCTL fragments, a sound and a complete one. We show
that safety properties only have finite counterexamples, whereas liveness
properties have none. We compare our characterisation for qualitative
properties with the one for branching time properties by Manolios and Trefler,
and present sound and complete PCTL fragments for characterising the notions of
strong safety and absolute liveness coined by Sistla
- …