2,581 research outputs found
Ground states of quantum kagome antiferromagnets in a magnetic field
We study the ground state properties of a quantum antiferromagnet in the
kagome lattice in the presence of a magnetic field, paying particular attention
to the stability of the plateau at magnetization 1/3 of saturation. While the
plateau is reinforced by certain deformations of the lattice, like the
introduction of structural defect lines and against an Ising anisotropy, ground
state correlations are seen to be quite different and the undistorted SU(2)
case appears to be rather special.Comment: 3 pages, 3 figures, contribution to the Japanese-French symposium on
"Quantum magnetism in spin, charge and orbital systems", Paris 1-4 October
200
Creating agent platforms to host agent-mediated services that share resources
After a period where the Internet was exclusively filled with content,
the present
efforts are moving towards services, which handle the raw information to
create
value from it. Therefore labors to create a wide collection of
agent-based services
are being perfomed in several projects, such as Agentcities does.
In this work we present an architecture for agent platforms named
a-Buildings. The
aim of the proposed architecture is to ease the creation, installation,
search and
management of agent-mediated services and the share of resources among
services.
To do so the a-Buildings architecture creates a new level of abstraction
on top of
the standard FIPA agent platform specification.
Basically, an a-Building is a service-oriented platform which offers a
set of
low level services to the agents it hosts. We define low level services
as those
required services that are neccesary to create more complex high level
composed
services.Postprint (published version
Quantum kagome antiferromagnet in a magnetic field: Low-lying non-magnetic excitations versus valence-bond crystal order
We study the ground state properties of a quantum antiferromagnet on the
kagome lattice in the presence of a magnetic field, paying particular attention
to the stability of the plateau at magnetization 1/3 of saturation and the
nature of its ground state. We discuss fluctuations around classical ground
states and argue that quantum and classical calculations at the harmonic level
do not lead to the same result in contrast to the zero-field case. For spin
S=1/2 we find a magnetic gap below which an exponential number of non-magnetic
excitations are present. Moreover, such non-magnetic excitations also have a
(much smaller) gap above the three-fold degenerate ground state. We provide
evidence that the ground state has long-range order of valence-bond crystal
type with nine spins in the unit cell.Comment: 5 pages including 4 figures, uses REVTeX4; final version with some
small extensions; to appear in Phys. Rev.
Non-Abelian Bosonization and Haldane's Conjecture
We study the long wavelength limit of a spin S Heisenberg antiferromagnetic chain. The fermionic Lagrangian obtained corresponds to a perturbed level 2S SU(2) Wess-Zumino-Witten model. This effective theory is then mapped into a compact U(1) boson interacting with Z_{2S} parafermions. The analysis of this effective theory allows us to show that when S is an integer there is a mass gap to all excitations, whereas this gap vanishes in the half-odd-integer spin case. This gives a field theory treatment of the so-called Haldane's conjecture for arbitrary values of the spin S
Magnetization plateaux in the classical Shastry-Sutherland lattice
We investigated the classical Shastry-Sutherland lattice under an external
magnetic field in order to understand the recently discovered magnetization
plateaux in the rare-earth tetraborides compounds RB. A detailed study of
the role of thermal fluctuations was carried out by mean of classical spin
waves theory and Monte-Carlo simulations. Magnetization quasi-plateaux were
observed at 1/3 of the saturation magnetization at non zero temperature. We
showed that the existence of these quasi-plateaux is due to an entropic
selection of a particular collinear state. We also obtained a phase diagram
that shows the domains of existence of different spin configurations in the
magnetic field versus temperature plane.Comment: 4 pages, proceedings of HFM200
Recommended from our members
Hubbard ladders in a magnetic field
The behavior of a two leg Hubbard ladder in the presence of a magnetic field is studied by means of Abelian bosonization. We predict the appearance of a new (doping dependent) plateau in the magnetization curve of a doped 2-leg spin ladder in a wide range of couplings. We also discuss the extension to N-leg Hubbard ladders
Nouvelles données sur le Miocène moyen marin ("Sallomacien") de Gironde (Bassin d'Aquitaine-France) Approche des paléoenvironnements New data about the maine Middle Miocene ("Sallomacian") of Gironde (Aquitaine Basin); paleoecological outline
The Mid Miocene marine formations of Salles area (former "Sallomacian" stage) have been studied again from numerous outcrops
and cores. The deep structural framework influences notably of the characteristics and distribution of the deposits, which are
neritic. The stratigraphy is stated precisely thanks to the planktonic fauna and floradetailed examination (probably Serravallian zones NN6 - N12). Several paleobiofacies are reconstituted from the rich invertebrate faunas, which give also paleoclimatic data
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