190 research outputs found
Role of the attractive intersite interaction in the extended Hubbard model
We consider the extended Hubbard model in the atomic limit on a Bethe lattice
with coordination number z. By using the equations of motion formalism, the
model is exactly solved for both attractive and repulsive intersite potential
V. By focusing on the case of negative V, i.e., attractive intersite
interaction, we study the phase diagram at finite temperature and find, for
various values of the filling and of the on-site coupling U, a phase transition
towards a state with phase separation. We determine the critical temperature as
a function of the relevant parameters, U/|V|, n and z and we find a reentrant
behavior in the plane (U/|V|,T). Finally, several thermodynamic properties are
investigated near criticality.Comment: 7 pages, 7 figures. EPJB Topical Issue on Novel Quantum Phases and
Mesoscopic Physics in Quantum Gase
New Results on the Phase Diagram of the FFXY Model: A Twisted CFT Approach
The issue of the number, nature and sequence of phase transitions in the
fully frustrated XY (FFXY) model is a highly non trivial one due to the complex
interplay between its continuous and discrete degrees of freedom. In this
contribution we attack such a problem by means of a twisted conformal field
theory (CFT) approach and show how it gives rise to the U (1)
symmetry and to the whole spectrum of excitations of the FFXY model.Comment: 7 pages; talk given by G. Niccoli at "Path Integrals - New Trends and
Perspectives International Conference", Max-Planck-Institut, Dresden,
Germany, September 23 - 28, 200
Quantum phase excitations in Ginzburg-Landau superconductors
We give a straightforward generalization of the Ginzburg-Landau theory for
superconductors where the scalar phase field is replaced by an antisymmetric
Kalb-Ramond field. We predict that at very low temperatures, where quantum
phase effects are expected to play a significant role, the presence of vortices
destroys superconductivity.Comment: revtex, 4 pages, no figure
Recommended from our members
Now is the time for a comfort congress
When buying a bed, a chair or a car, taking the train, holding a hand tool or flying across the ocean,
comfort comes into play. Users interact with products and rate their experience. Therefore,
designers and manufacturers of products such as seats, cars, beds, hand tools, and production lines
strive for optimal comfort. If we look at some trends like “attention to health”, “ageing workforce
(and population)”, “environmental awareness and sustainability” and “attention to well-being”,
(dis)comfort is an important consideration (Vink & Hallbeck, 2012). This means that in our daily
lives we are confronted with comfort
Topological order in Josephson junction ladders with Mobius boundary conditions
We propose a CFT description for a closed one-dimensional fully frustrated
ladder of quantum Josephson junctions with Mobius boundary conditions, in
particular we show how such a system can develop topological order. Such a
property is crucial for its implementation as a "protected" solid state qubit.Comment: 14 pages, 3 figures, to appear in JSTA
Morphological, rheological and electrical properties of composites filled with carbon nanotubes functionalized with 1-pyrenebutyric acid
Non-covalent functionalization of Multi Wall Carbon Nanotubes (MWCNTs) could provide a solution for preserving their electronic structure facilitating the nanocomposite process preparation. Functionalization of MWCNTs by π-stacking interaction between nanofiller and a pyrene derivative has been explored. The rheological properties of filled epoxy resins highlight very interesting benefits from this kind of functionalization. Besides its peculiar capability for preventing agglomeration in the nanofiller dispersion step, it also efficiently contributes to a decrease in the viscosity of the nanocomposites; hence contrasting one of the most relevant drawback related to the manufacturing processes of the nanocomposites at MWCNTs loading rates beyond the Electrical Percolation Threshold (EPT). Because no damage of MWCNTs occurs, sp2 hybridization of carbon atoms is preserved together with the π-electron delocalization typical of polynuclear aromatic rings. Consequently, no deterioration in the electrical properties are detected; the measured EPT values are typical of nanocomposites containing embedded unfunctionalized MWCNTs (lower than 0.28 wt%), whereas for the electrical conductivity beyond the EPT, an enhancement is observed
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Integrating and applying models of comfort
This paper gives an overview of the relevance of the comfort concept, its definitions, boundary conditions, and stakeholders. Current comfort theories are presented and reflected on, both in their applicability and testing methodology. Questionnaires commonly used to study comfort and discomfort are also reviewed. An example of a comfort lab is introduced in its functionality and tools, which can be useful as a benchmark for others studying comfort
Dissipative quantum mechanics and Kondo-like impurities on noncommutative two-tori
In a recent paper, by exploiting the notion of Morita equivalence for field
theories on noncommutative tori and choosing rational values of the
noncommutativity parameter (in appropriate units), a general
one-to-one correspondence between the -reduced conformal field theory (CFT)
describing a quantum Hall fluid (QHF) at paired states fillings and an Abelian noncommutative field theory (NCFT) has been
established . That allowed us to add new evidence to the relationship between
noncommutativity and quantum Hall fluids\cite% {ncmanybody}. On the other hand,
the -reduced CFT is equivalent to a system of two massless scalar bosons
with a magnetic boundary interaction as introduced by Callan et al., at the so
called ``magic''\ points. We are then able to describe, within such a
framework, the dissipative quantum mechanics of a particle confined to a plane
and subject to an external magnetic field normal to it. Here we develop such a
point of view by focusing on the case which corresponds to a quantum Hall
bilayer. The key role of a localized impurity which couples the two layers is
emphasized and the effect of noncommutativity in terms of generalized magnetic
translations (GMT) is fully exploited. As a result, general GMT operators are
introduced, in the form of a tensor product, which act on the QHF and defect
space respectively, and a comprehensive study of their rich structure is
performed.Comment: 18 pages, 1 figure, accepted for publication in International Journal
of Modern Physics
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