12,243 research outputs found
Rashba spin-orbit interaction in graphene armchair nanoribbons
We study graphene nanoribbons (GNRs) with armchair edges in the presence of
Rashba spin-orbit interaction (RSOI). We impose the boundary conditions on the
tight binding Hamiltonians for bulk graphene with RSOI by means of a sine
transform and study in detail the influence of RSOI on the spectra and the spin
polarization. We show that the spin polarization perpendicular to the GNR
changes sign when reversing the momentum along the GNR if the bands are coupled
by strong RSOI. Furthermore, we derive a linearized approximation to the RSOI
Hamiltonian and find that only the neighboring modes of an energy band have to
be taken into account in order to achieve a good approximation for the same
band. Due to their experimental availability and various proposals for
engineering appropriate RSOI, GNRs with armchair edges are a promising
candidate for possible spintronics applications.Comment: added journal reference, small updates, 9 pages, 8 figure
Signatures of Confinement in Axial Gauge QCD
A comparative dynamical study of axial gauge QED and QCD is presented.
Elementary excitations associated with particular field configurations are
investigated. Gluonic excitations analogous to linearly polarized photons are
shown to acquire infinite energy. Suppression of this class of excitations in
QCD results from quantization of the chromelectric flux and is interpreted as a
dual Meissner effect, i.e. as expulsion from the QCD vacuum of chromo-electric
fields which are constant over significant distances. This interpretation is
supported by a comparative evaluation of the interaction energy of static
charges in the axial gauge representation of QED and QCD.Comment: 22 pages (no figures
Confinement from Instantons or Merons
In contrast to ensembles of singular gauge instantons, which are well known
to fail to produce confinement, it is shown that effective theories based on
ensembles of merons or regular gauge instantons do produce confinement.
Furthermore, when the scale is set by the string tension, the action density,
topological susceptibility, and glueball masses are similar to those arising in
lattice QCD.Comment: 3 pages, 5 figures. Talk given at Lattice2004 (topology and
confinement) Fermilab June 21-26, 200
Analysis of light scattering off photonic crystal slabs in terms of Feshbach resonances
Techniques to deal with Feshbach resonances are applied to describe resonant
light scattering off one dimensional photonic crystal slabs. Accurate
expressions for scattering amplitudes, free of any fitting parameter, are
obtained for isolated as well as overlapping resonances. They relate the
resonance properties to the properties of the optical structure and of the
incident light. For the most common case of a piecewise constant dielectric
function, the calculations can be carried out essentially analytically. After
establishing the accuracy of this approach we demonstrate its potential in the
analysis of the reflection coefficients for the diverse shapes of overlapping,
interacting resonances.Comment: 12 pages, 5 figure
Quantum Electrodynamics in the Light-Front Weyl Gauge
We examine QED(3+1) quantised in the `front form' with finite `volume'
regularisation, namely in Discretised Light-Cone Quantisation. Instead of the
light-cone or Coulomb gauges, we impose the light-front Weyl gauge . The
Dirac method is used to arrive at the quantum commutation relations for the
independent variables. We apply `quantum mechanical gauge fixing' to implement
Gau{\ss}' law, and derive the physical Hamiltonian in terms of unconstrained
variables. As in the instant form, this Hamiltonian is invariant under global
residual gauge transformations, namely displacements. On the light-cone the
symmetry manifests itself quite differently.Comment: LaTeX file, 30 pages (A4 size), no figures. Submitted to Physical
review D. January 18, 1996. Originally posted, erroneously, with missing
`Weyl' in title. Otherwise, paper is identica
Scaling Invariance in a Time-Dependent Elliptical Billiard
We study some dynamical properties of a classical time-dependent elliptical
billiard. We consider periodically moving boundary and collisions between the
particle and the boundary are assumed to be elastic. Our results confirm that
although the static elliptical billiard is an integrable system, after to
introduce time-dependent perturbation on the boundary the unlimited energy
growth is observed. The behaviour of the average velocity is described using
scaling arguments
The Center-Symmetric Phase of QCD
An investigation of the center symmetric phase of SU(2) QCD is presented. The
role of the center-symmetry, the dynamics of Polyakov loops and the structure
of Abelian monopoles are studied within the axial gauge representation of QCD.
Realization of the center symmetry is shown to result from non-perturbative
gauge fixing and concomitant confinement like properties emerging even at the
perturbative level are displayed. In an analysis of the Polyakov loop dynamics,
non-perturbative gauge fixing is also shown to inevitably lead to singular
gauge field configurations whose dynamics are briefly discussed.Comment: 14 pages, Latex. To appear in the Proceedings of the 3rd Workshop on
''Continuous Advances in QCD'', Minneapolis, April 16-19, 199
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