6,216 research outputs found
Incipient quantum melting of the one-dimensional Wigner lattice
A one--dimensional tight--binding model of electrons with long--range Coulomb
interactions is studied in the limit where double site occupancy is forbidden
and the Coulomb coupling strength is large with respect to the hopping
amplitude . The quantum problem of a kink--antikink pair generated in the
Wigner lattice (the classical ground state for ) is solved for fillings
, where is an integer larger than 1. The pair energy becomes
negative for a relatively high value of , . This signals
the initial stage of the quantum melting of the Wigner lattice
Variational Wave Function for Generalized Wigner Lattices in One Dimension
We study a system of electrons on a one-dimensional lattice, interacting
through the long range Coulomb forces, by means of a variational technique
which is the strong coupling analog of the Gutzwiller approach. The problem is
thus the quantum version of Hubbard's classical model of the generalized Wigner
crystal [J. Hubbard, Phys. Rev. B 17, 494 (1978)]. The magnetic exchange energy
arising from quantum fluctuations is calculated, and turns out to be smaller
than the energy scale governing charge degrees of freedom. This approach could
be relevant in insulating quasi-one-dimensional compounds where the long range
Coulomb interactions are not screened. In these compounds charge order often
appears at high temperatures and coexists with magnetic order at low
temperatures.Comment: 4 pages, proceedings of ECRYS-200
Bosonized supersymmetry from the Majorana-Dirac-Staunton theory and massive higher-spin fields
We propose a (3+1)D linear set of covariant vector equations, which unify the
spin 0 ``new Dirac equation'' with its spin 1/2 counterpart, proposed by
Staunton. Our equations describe a spin (0,1/2) supermultiplet with different
numbers of degrees of freedom in the bosonic and fermionic sectors. The
translation-invariant spin deegres of freedom are carried by two copies of the
Heisenberg algebra. This allows us to realize space-time supersymmetry in a
bosonized form. The grading structure is provided by an internal reflection
operator. Then the construction is generalized by means of the Majorana
equation to a supersymmetric theory of massive higher-spin particles. The
resulting theory is characterized by a nonlinear symmetry superalgebra, that,
in the large-spin limit, reduces to the super-Poincare algebra with or without
tensorial central charge.Comment: 21 pages; refs added, version accepted for publication in Physical
Review
Supersymmetry between Jackiw-Nair and Dirac-Majorana anyons
The Jackiw-Nair description of anyons combines spin-1 topologically massive
fields with the discrete series representation of the Lorentz algebra, which
has fractional spin. In the Dirac-Majorana formulation the spin-1 part is
replaced by the spin 1/2 planar Dirac equation. The two models are shown to
belong to an N=1 supermultiplet, which carries a super-Poincare symmetry.Comment: 4 pages, no figures. Typos corrected. Published versio
Measuring the interaction force between a high temperature superconductor and a permanent magnet
Repulsive and attractive forces are both possible between a superconducting
sample and a permanent magnet, and they can give place to magnetic levitation
or free-suspension phenomena, respectively. We show experiments to quantify
this magnetic interaction which represents a promising field regarding to
short-term technological applications of high temperature superconductors. The
measuring technique employs an electronic balance and a rare-earth magnet that
induces a magnetic moment in a melt-textured YBa2Cu3O7 superconductor immersed
in liquid nitrogen. The simple design of the experiments allows a fast and easy
implementation in the advanced physics laboratory with a minimum cost. Actual
levitation and suspension demonstrations can be done simultaneously as a help
to interpret magnetic force measurements.Comment: 12 pages and 3 figures in postscrip
Oscillatory dynamics of a superconductor vortex lattice in high amplitude ac magnetic fields
In this work we study by ac susceptibility measurements the evolution of the
solid vortex lattice mobility under oscillating forces. Previous work had
already shown that in YBCO single crystals, below the melting transition, a
temporarily symmetric magnetic ac field (e.g. sinusoidal, square, triangular)
can heal the vortex lattice (VL) and increase its mobility, but a temporarily
asymmetric one (e.g. sawtooth) of the same amplitude can tear the lattice into
a more pinned disordered state. In this work we present evidence that the
mobility of the VL is reduced for large vortex displacements, in agreement with
predictions of recent simulations. We show that with large symmetric
oscillating fields both an initially ordered or an initially disordered VL
configuration evolve towards a less mobile lattice, supporting the scenario of
plastic flow.Comment: 5 pages, 4 figures. To appear in Phys. Rev.
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Against wasted politics: a critique of the circular economy
The discourse of zero-waste and the circular economy has been championed by key players, such as the European Commission, management consultancies, NGOs, academics and multinational companies, in recent years. Given the all too obvious social and environmental crises associated with out-of-bounds growth capitalism, the circular
economy has been one of the main references for rebuilding and reforming a political economy of sustainable growth. In this paper we detect a de-politicizing strategy in this attempt of reform, and, consequently, aim at re-locating a position for the politicization of growth-driven capitalism and the circular economy. We do this by offering a unique
discursive-material theoretical framework, bringing together Marxist and Lacanian psychoanalytic readings. This will allow understanding both the subjective relation with the meaning of waste and the material exchanges that place the subject in the position to
produce and consume waste as a valuable commodity. In our quest to (re-)politicize waste, we offer three practical steps that aim at interrupting the endless repetition of
waste, which include attempts to eradicate it. This argument will be illustrated by making reference to the circular strategies of Apple Inc., the world’s largest and most iconic consumer electronics company
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