414 research outputs found
Phase diagrams of vortex matter with multi-scale inter-vortex interactions in layered superconductors
It was recently proposed to use the stray magnetic fields of superconducting
vortex lattices to trap ultracold atoms for building quantum emulators. This
calls for new methods for engineering and manipulating of the vortex states.
One of the possible routes utilizes type-1.5 superconducting layered systems
with multi-scale inter-vortex interactions. In order to explore the possible
vortex states that can be engineered, we present two phase diagrams of
phenomenological vortex matter models with multi-scale inter-vortex
interactions featuring several attractive and repulsive length scales. The
phase diagrams exhibit a plethora of phases, including conventional 2D lattice
phases, five stripe phases, dimer, trimer, and tetramer phases, void phases,
and stable low-temperature disordered phases. The transitions between these
states can be controlled by the value of an applied external field.Comment: 16 pages, 20 figure
Magnetism and pairing of two-dimensional trapped fermions
The emergence of local phases in a trapped two-component Fermi gas in an
optical lattice is studied using quantum Monte Carlo simulations. We treat
temperatures that are comparable or lower than those presently achievable in
experiments and large enough systems that both magnetic and paired phases can
be detected by inspection of the behavior of suitable short-range correlations.
We use the latter to suggest the interaction strength and temperature range at
which experimental observation of incipient magnetism and d-wave pairing are
more likely and evaluate the relation between entropy and temperature in
two-dimensional confined fermionic systems.Comment: 4 pages + supplementary materia
Kaleidoscope of exotic quantum phases in a frustrated XY model
The existence of quantum spin liquids was first conjectured by Pomeranchuk
some 70 years ago, who argued that frustration in simple antiferromagnetic
theories could result in a Fermi-liquid-like state for spinon excitations. Here
we show that a simple quantum spin model on a honeycomb lattice hosts the long
sought for Bose metal with a clearly identifiable Bose surface. The complete
phase diagram of the model is determined via exact diagonalization and is shown
to include four distinct phases separated by three quantum phase transitions
Quantum Monte Carlo study of the visibility of one-dimensional Bose-Fermi mixtures
The study of ultracold optically trapped atoms has opened new vistas in the
physics of correlated quantum systems. Much attention has now turned to
mixtures of bosonic and fermionic atoms. A central puzzle is the disagreement
between the experimental observation of a reduced bosonic visibility , and quantum Monte Carlo (QMC) calculations which show
increasing. In this paper, we present QMC simulations which evaluate the
density profiles and of mixtures of bosons and fermions in
one-dimensional optical lattices. We resolve the discrepancy between theory and
experiment by identifying parameter regimes where is reduced, and
where it is increased. We present a simple qualitative picture of the different
response to the fermion admixture in terms of the superfluid and
Mott-insulating domains before and after the fermions are included. Finally, we
show that exhibits kinks which are tied to the domain evolution
present in the pure case, and also additional structure arising from the
formation of boson-fermion molecules, a prediction for future experiments.Comment: 4 pages, 6 figure
Static versus dynamic fluctuations in the one-dimensional extended Hubbard model
The extended Hubbard Hamiltonian is a widely accepted model for uncovering
the effects of strong correlations on the phase diagram of low-dimensional
systems, and a variety of theoretical techniques have been applied to it. In
this paper the world-line quantum Monte Carlo method is used to study spin,
charge, and bond order correlations of the one-dimensional extended Hubbard
model in the presence of coupling to the lattice. A static alternating lattice
distortion (the ionic Hubbard model) leads to enhanced charge density wave
correlations at the expense of antiferromagnetic order. When the lattice
degrees of freedom are dynamic (the Hubbard-Holstein model), we show that a
similar effect occurs even though the charge asymmetry must arise
spontaneously. Although the evolution of the total energy with lattice coupling
is smooth, the individual components exhibit sharp crossovers at the phase
boundaries. Finally, we observe a tendency for bond order in the region between
the charge and spin density wave phases.Comment: Corrected typos. (10 pages, 9 figures
Performance of air-cooled organic Rankine cycle plants using temperature distributions from arid parts of South Australia
GeoCat; 74874Air-cooling is necessary for geothermal plays in dry areas and ambient air temperature significantly affects the power output of air-cooled thermal power plants. Hence, a method for determining the effect of ambient air temperature on subcritical and supercritical, air-cooled binary Rankine cycles using moderate temperature geothermal fluid and various working fluids is presented. Part of this method, includes a method for maximizing working fluid flow from a supercritical heat exchanger. In the example presented isobutane is used as the working fluid, while the geothermal fluid temperature and flowrate are set at 150°C and 126kg/s. Results of this analysis show that for every 14°C increase in ambient air temperature, above the ambient temperature used for design purposes, there is ~20% loss in brine efficiency; while conversely, there is no gain in brine efficiency for any drop in ambient air temperature below the ambient air temperature used for design purposes. Using the ambient air temperature distribution from Leigh Creek, Australia, this analysis shows that an optimally designed plant produces 6% more energy annually than a plant designed using the mean ambient temperature.J.J. Varney and N. Bea
Building a model to investigate the effect of varying ambient air temperature on air-cooled organic Rankine cycle plant performance
GeoCat; 74874Air-cooling is necessary for geothermal plays in dry areas and ambient air temperature significantly affects the power output of air-cooled thermal power plants. Hence, a method for determining the effect of ambient air temperature on subcritical and supercritical, air-cooled binary Rankine cycles using moderate temperature geothermal fluid and various working fluids is presented. Part of this method, includes a method for maximizing working fluid flow from a supercritical heat exchanger. In the example presented isobutane is used as the working fluid, while the geothermal fluid temperature and flowrate are set at 150°C and 126kg/s. Results of this analysis show that for every 14°C increase in ambient air temperature, above the ambient temperature used for design purposes, there is ~20% loss in brine efficiency; while conversely, there is no gain in brine efficiency for any drop in ambient air temperature below the ambient air temperature used for design purposes. Using the ambient air temperature distribution from Leigh Creek, Australia, this analysis shows that an optimally designed plant produces 6% more energy annually than a plant designed using the mean ambient temperature.J.J. Varney and N. Bea
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