10,137 research outputs found
The Fractional Quantum Hall effect in an array of quantum wires
We demonstrate the emergence of the quantum Hall (QH) hierarchy in a 2D model
of coupled quantum wires in a perpendicular magnetic field. At commensurate
values of the magnetic field, the system can develop instabilities to
appropriate inter-wire electron hopping processes that drive the system into a
variety of QH states. Some of the QH states are not included in the
Haldane-Halperin hierarchy. In addition, we find operators allowed at any field
that lead to novel crystals of Laughlin quasiparticles. We demonstrate that any
QH state is the groundstate of a Hamiltonian that we explicitly construct.Comment: Revtex, 4 pages, 2 figure
Charge order, superconductivity, and a global phase diagram of doped antiferromagnets
We investigate the interplay between lattice-symmetry breaking and
superconducting order in a two-dimensional model of doped antiferromagnets,
with long-range Coulomb interactions and Sp(2N) spin symmetry, in the large-N
limit. Our results motivate the outline of a global phase diagram for the
cuprate superconductors. We describe the quantum transitions between the
phases, the evolution of their fermion excitation spectrum, and the
experimental implications.Comment: 4 pages, 4 figs, final version as publishe
A Local Moment Approach to magnetic impurities in gapless Fermi systems
A local moment approach is developed for the single-particle excitations of a
symmetric Anderson impurity model (AIM), with a soft-gap hybridization
vanishing at the Fermi level with a power law r > 0. Local moments are
introduced explicitly from the outset, and a two-self-energy description is
employed in which the single-particle excitations are coupled dynamically to
low-energy transverse spin fluctuations. The resultant theory is applicable on
all energy scales, and captures both the spin-fluctuation regime of strong
coupling (large-U), as well as the weak coupling regime. While the primary
emphasis is on single particle dynamics, the quantum phase transition between
strong coupling (SC) and (LM) phases can also be addressed directly; for the
spin-fluctuation regime in particular a number of asymptotically exact results
are thereby obtained. Results for both single-particle spectra and SC/LM phase
boundaries are found to agree well with recent numerical renormalization group
(NRG) studies. A number of further testable predictions are made; in
particular, for r < 1/2, spectra characteristic of the SC state are predicted
to exhibit an r-dependent universal scaling form as the SC/LM phase boundary is
approached and the Kondo scale vanishes. Results for the `normal' r = 0 AIM are
moreover recovered smoothly from the limit r -> 0, where the resultant
description of single-particle dynamics includes recovery of Doniach-Sunjic
tails in the Kondo resonance, as well as characteristic low-energy Fermi liquid
behaviour.Comment: 52 pages, 19 figures, submitted to Journal of Physics: Condensed
Matte
Andreev tunnelling in quantum dots: A slave-boson approach
We study a strongly interacting quantum dot connected to a normal and to a
superconducting lead. By means of the slave-boson technique we investigate the
low temperature regime and discuss electrical transport through the dot. We
find that the zero bias anomaly in the current-voltage characteristics which is
associated to the occurance of the Kondo resonance in the quantum dot, is
enhanced in the presence of superconductivity, due to resonant Andreev
scattering.Comment: 4 pages, 1 figur
‘‘Lozenge’’ contour plots in scattering from polymer networks
We present a consistent explanation for the appearance of “lozenge” shapes in contour plots of the two dimensional scattering intensity from stretched polymer networks. By explicitly averaging over quenched variables in a tube model, we show that lozenge patterns arise as a result of chain material that is not directly deformed by the stretch. We obtain excellent agreement with experimental data
Nonlinear Dynamics of Composite Fermions in Nanostructures
We outline a theory describing the quasi-classical dynamics of composite
fermions in the fractional quantum Hall regime in the potentials of arbitrary
nanostructures. By an appropriate parametrization of time we show that their
trajectories are independent of their mass and dispersion. This allows to study
the dynamics in terms of an effective Hamiltonian although the actual
dispersion is as yet unknown. The applicability of the theory is verified in
the case of antidot arrays where it explains details of magnetoresistance
measurements and thus confirms the existence of these quasiparticles.Comment: submitted to Europhys. Lett., 4 pages, postscrip
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