8,532 research outputs found
Gauge approach to superfluid density in underdoped cuprates
We prove that a gauge approach based on a composite structure of the hole in
hole-doped cuprates is able to capture analytically many features of the
experimental data on superfluid density in the moderate-underdoping to
nearly-optimal doping region, including critical exponent, the Uemura relation
and near universality of the normalized superfluid density.Comment: 13 pages, 2 figures, accepted for publication in EP
Interacting branes, dual branes, and dyonic branes: a unifying lagrangian approach in D dimensions
This paper presents a general covariant lagrangian framework for the dynamics
of a system of closed n-branes and dual (D-n-4)-branes in D dimensions,
interacting with a dynamical (n+1)-form gauge potential. The framework proves
sufficiently general to include also a coupling of the branes to (the bosonic
sector of) a dynamical supergravity theory. We provide a manifestly
Lorentz-invariant and S-duality symmetric Lagrangian, involving the (n+1)-form
gauge potential and its dual (D-n-3)-form gauge potential in a symmetric way.
The corresponding action depends on generalized Dirac-strings. The requirement
of string-independence of the action leads to Dirac-Schwinger quantization
conditions for the charges of branes and dual branes, but produces also
additional constraints on the possible interactions. It turns out that a system
of interacting dyonic branes admits two quantum mechanically inequivalent
formulations, involving inequivalent quantization conditions. Asymmetric
formulations involving only a single vector potential are also given. For the
special cases of dyonic branes in even dimensions known results are easily
recovered. As a relevant application of the method we write an effective action
which implements the inflow anomaly cancellation mechanism for interacting
heterotic strings and five-branes in D=10. A consistent realization of this
mechanism requires, in fact, dynamical p-form potentials and a systematic
introduction of Dirac-strings.Comment: 36 pages, LaTeX, no figure
Superfluid density in cuprates: hints on gauge compositeness of the holes
We show that several features (the three-dimensional XY universality for
moderate underdoping, the almost-BCS behaviour for moderate overdoping and the
critical exponent) of the superfluid density in hole-doped cuprates hint at a
composite structure of the holes. This idea can be implemented in a spin-charge
gauge approach to the model and provides indeed good agreement
with available experimental data.Comment: 5 pages, 1 figure, to be published in the proceedings of the
International Conference in Superconductivty and Magnetism ICSM201
A gauge approach to the "pseudogap" phenomenology of the spectral weight in high Tc cuprates
We assume the t-t'-J model to describe the CuO_2 planes of hole-doped
cuprates and we adapt the spin-charge gauge approach, previously developed for
the t-J model, to describe the holes in terms of a spinless fermion carrying
the charge (holon) and a neutral boson carrying spin 1/2 (spinon), coupled by a
slave-particle gauge field. In this framework we consider the effects of a
finite density of incoherent holon pairs in the normal state. Below a crossover
temperature, identified as the experimental "upper pseudogap", the scattering
of the "quanta" of the phase of the holon-pair field against holons reproduces
the phenomenology of Fermi arcs coexisting with gap in the antinodal region. We
thus obtain a microscopic derivation of the main features of the hole spectra
due to pseudogap. This result is obtained through a holon Green function which
follows naturally from the formalism and analytically interpolates between a
Fermi liquid-like and a d-wave superconductor behavior as the coherence length
of the holon pair order parameter increases. By inserting the gauge coupling
with the spinon we construct explicitly the hole Green function and calculate
its spectral weight and the corresponding density of states. So we prove that
the formation of holon pairs induces a depletion of states on the hole Fermi
surface. We compare our results with ARPES and tunneling experimental data. In
our approach the hole preserves a finite Fermi surface until the
superconducting transition, where it reduces to four nodes. Therefore we
propose that the gap seen in the normal phase of cuprates is due to the thermal
broadening of the SC-like peaks masking the Fermi-liquid peak. The Fermi arcs
then correspond to the region of the Fermi surface where the Fermi-liquid peak
is unmasked.Comment: 10 figures, comments and references added, 2 figures change
Spin-statistics transmutation in relativistic quantum field theories of dyons
We analyse spin and statistics of quantum dyon fields, i.e. fields carrying
both electric and magnetic charge, in 3+1 space-time dimensions. It has been
shown long time ago that, at the quantum mechanical level, a composite dyon
made out of a magnetic pole of charge g and a particle of electric charge e
possesses half-integral spin and fermionic statistics, if the constituents are
bosons and the Dirac quantization condition holds, with n odd. This
phenomenon is called spin-statistics transmutation. We show that the same
phenomenon occurs at the quantum field theory level for an elementary dyon.
This analysis requires the construction of gauge invariant charged dyon fields.
Dirac's proposal for such fields, relying on a Coulomb-like photon cloud, leads
to quantum correlators exhibiting an unphysical dependence on the Dirac-string.
Recently Froehlich and Marchetti proposed a recipe for charged dyon fields,
based on a sum over Mandelstam-strings, which overcomes this problem. Using
this recipe we derive explicit expressions for the quantum field theory
correlators and we provide a proof of the occurrence of spin-statistics
transmutation. The proof reduces to a computation of the self-linking numbers
of dyon worldlines and Mandelstam strings, projected on a fixed time
three-space. Dyon composites are also analysed. The transmutation discussed in
this paper bares some analogy with the appearance of anomalous spin and
statistics for particles or vortices in Chern-Simons theories in 2+1
dimensions. However, peculiar features appear in 3+1 dimensions e.g. in the
spin addition rule.Comment: 32 pages, LaTeX, no figure
Monopole fields from vortex sheets reconciling Abelian and center dominance
We describe a new order parameter for the confinement-deconfinement
transition in lattice SU(2) Yang-Mills theory. It is expressed in terms of
magnetic monopole field correlators represented as sums over sheets of center
vortices. Our construction establishes a link between "abelian" and "center
dominance". It avoids an inconsistency in the treatment of small scales present
in earlier definitions of monopole fields by respecting Dirac's quantization
condition for magnetic fluxes.Comment: LaTeX file, 6 pages; Lattice2001(plenary
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