6,835 research outputs found
Non Abelian Sugawara Construction and the q-deformed N=2 Superconformal Algebra
The construction of a q-deformed N=2 superconformal algebra is proposed in
terms of level 1 currents of quantum affine
Lie algebra and a single real Fermi field. In particular, it suggests the
expression for the q-deformed Energy-Momentum tensor in the Sugawara form. Its
constituents generate two isomorphic quadratic algebraic structures. The
generalization to is also proposed.Comment: AMSLATEX, 21page
The Algebra of the Energy-Momentum Tensor and the Noether Currents in Classical Non-Linear Sigma Models
The recently derived current algebra of classical non-linear sigma models on
arbitrary Riemannian manifolds is extended to include the energy-momentum
tensor. It is found that in two dimensions the energy-momentum tensor
, the Noether current associated with the global
symmetry of the theory and the composite field appearing as the coefficient
of the Schwinger term in the current algebra, together with the derivatives of
and , generate a closed algebra. The subalgebra generated by the
light-cone components of the energy-momentum tensor consists of two commuting
copies of the Virasoro algebra, with central charge , reflecting
the classical conformal invariance of the theory, but the current algebra part
and the semidirect product structure are quite different from the usual
Kac-Moody / Sugawara type construction.Comment: 10 pages, THEP 92/2
Isotope effect in quasi-two-dimensional metal-organic antiferromagnets
Although the isotope effect in superconducting materials is well-documented,
changes in the magnetic properties of antiferromagnets due to isotopic
substitution are seldom discussed and remain poorly understood. This is perhaps
surprising given the possible link between the quasi-two-dimensional (Q2D)
antiferromagnetic and superconducting phases of the layered cuprates. Here we
report the experimental observation of shifts in the N\'{e}el temperature and
critical magnetic fields (; ) in a Q2D organic molecular antiferromagnets on
substitution of hydrogen for deuterium. These compounds are characterized by
strong hydrogen bonds through which the dominant superexchange is mediated. We
evaluate how the in-plane and inter-plane exchange energies evolve as the
hydrogens on different ligands are substituted, and suggest a possible
mechanism for this effect in terms of the relative exchange efficiency of
hydrogen and deuterium bonds
Weak gauge principle and electric charge quantization
Starting from a weak gauge principle we give a new and critical revision of
the argument leading to charge quantization on arbitrary spacetimes. The main
differences of our approach with respect to previous works appear on spacetimes
with non trivial torsion elements on its second integral cohomology group. We
show that in these spacetimes there can be topologically non-trivial
configurations of charged fields which do not imply charge quantization.
However, the existence of a non-exact electromagnetic field always implies the
quantization of charges. Another consequence of the theory for spacetimes with
torsion is the fact that it gives rise to two natural quantization units that
could be identified with the electric quantization unit (realized inside the
quarks) and with the electron charge. In this framework the color charge can
have a topological origin, with the number of colors being related to the order
of the torsion subgroup. Finally, we discuss the possibility that the
quantization of charge may be due to a weak non-exact component of the
electromagnetic field extended over cosmological scales.Comment: Latex2e, 24 pages, no figure
Persistence to high temperatures of interlayer coherence in an organic superconductor
The interlayer magnetoresistance of the organic metal \cuscn is
studied in fields of up to 45 T and at temperatures from 0.5 K to 30 K. The
peak in seen in in-plane fields, a definitive signature of
interlayer coherence, remains to s exceeding the Anderson criterion for
incoherent transport by a factor . Angle-dependent magnetoresistance
oscillations are modeled using an approach based on field-induced quasiparticle
paths on a 3D Fermi surface, to yield the dependence of the scattering rate
. The results suggest that does not vary strongly over
the Fermi surface, and that it has a dependence due to electron-electron
scattering
Interacting Electrons and Localized Spins: Exact Results from Conformal Field Theory
We give a brief review of the Kondo effect in a one-dimensional interacting
electron system, and present exact results for the impurity thermodynamic
response based on conformal field theory.Comment: 6 pages LaTeX. To appear in the Proceedings of the 1995 Schladming
Winter School on Low-Dimensional Models in Statistical Physics and Quantum
Field Theor
Angle Dependent Magnetoresistance of the Layered Organic Superconductor \kappa-(ET)2Cu(NCS)2: Simulation and Experiment
The angle-dependences of the magnetoresistance of two different isotopic
substitutions (deuterated and undeuterated) of the layered organic
superconductor \kappa-(ET)2Cu(NCS)2 are presented. The angle dependent
magnetoresistance oscillations (AMRO) arising from the quasi-one-dimensional
(Q1D) and quasi-two-dimensional (Q2D) Fermi surfaces in this material are often
confused. By using the Boltzman transport equation extensive simulations of the
AMRO are made that reveal the subtle differences between the different species
of oscillation. No significant differences are observed in the electronic
parameters derived from quantum oscillations and AMRO for the two isotopic
substitutions. The interlayer transfer integrals are determined for both
isotopic substitutions and a slight difference is observed which may account
for the negative isotope effect previously reported [1]. The success of the
semi-classical simulations suggests that non-Fermi liquid effects are not
required to explain the interlayer-transport in this system.Comment: 15 pages, 16 figure
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