27,979 research outputs found
Universal Features of the Time Evolution of Evanescent Modes in a Left-Handed Perfect Lens
The time evolution of evanescent modes in Pendry's perfect lens proposal for
ideally lossless and homogeneous, left-handed materials is analyzed. We show
that time development of sub-wavelength resolution exhibits universal features,
independent of model details. This is due to the unavoidable near-degeneracy of
surface electromagnetic modes in the deep sub-wavelength region. By means of a
mechanical analog, it is shown that an intrinsic time scale (missed in
stationary studies) has to be associated with any desired lateral resolution. A
time-dependent cut-off length emerges, removing the problem of divergences
claimed to invalidate Pendry's proposal.Comment: 4 pages, 3 figures, title slightly changed, reference added, minor
correction
Measurement of anisotropies in the large-scale diffuse gamma-ray emission
We have performed the first measurement of the angular power spectrum in the
large-scale diffuse emission at energies from 1-50 GeV. We compared results
from data and a simulated model in order to identify significant differences in
anisotropy properties. We found angular power above the photon noise level in
the data at multipoles greater than ~ 100 for energies 1< E <10 GeV. The excess
power in the data suggests a contribution from a point source population not
present in the model.Comment: Contribution to SciNeGHE 2010, Trieste, Italy, September 2010; 4
pages, 5 figure
Plasmons and near-field amplification in double-layer graphene
We study the optical properties of double-layer graphene for linearly
polarized evanescent modes and discuss the in-phase and out-of-phase plasmon
modes for both, longitudinal and transverse polarization. We find a energy for
which reflection is zero, leading to exponentially amplified transmitted modes
similar to what happens in left-handed materials. For layers with equal
densities cm, we find a typical layer separation of
m to detect this amplification for transverse polarization
which may serve as an indirect observation of transverse plasmons. When the two
graphene layers lie on different chemical potentials, the exponential
amplification either follows the in-phase or out-of-phase plasmon mode
depending on the order of the low- and high-density layer. This opens up the
possibility of a tunable near-field amplifier or switch.Comment: 9 pages, 8 figure
B Mixing and Lifetimes at the Tevatron
The Tevatron collider at Fermilab provides a very rich environment for the
study of b-hadrons. Both the D0 and CDF experiments have collected a sample of
about 1 fb^{-1}. We report results on three topics: b-hadron lifetimes,
polarization amplitudes and the decay width difference in Bs to Jpsi Phi, and
Bs mixing.Comment: Flavor Physics & CP Violation Conference, Vancouver, 200
Invariant manifolds and orbit control in the solar sail three-body problem
In this paper we consider issues regarding the control and orbit transfer of solar sails in the circular restricted Earth-Sun system. Fixed points for solar sails in this system have the linear dynamical properties of saddles crossed with centers; thus the fixed points are dynamically unstable and control is required. A natural mechanism of control presents itself: variations in the sail's orientation. We describe an optimal controller to control the sail onto fixed points and periodic orbits about fixed points. We find this controller to be very robust, and define sets of initial data using spherical coordinates to get a sense of the domain of controllability; we also perform a series of tests for control onto periodic orbits. We then present some mission strategies involving transfer form the Earth to fixed points and onto periodic orbits, and controlled heteroclinic transfers between fixed points on opposite sides of the Earth. Finally we present some novel methods to finding periodic orbits in circumstances where traditional methods break down, based on considerations of the Center Manifold theorem
On Integrable Quantum Group Invariant Antiferromagnets
A new open spin chain hamiltonian is introduced. It is both integrable
(Sklyanin`s type matrices are used to achieve this) and invariant under
transformations in nilpotent irreps for
. Some considerations on the centralizer of nilpotent
representations and its representation theory are also presented.Comment: IFF-5/92, 13 pages, LaTex file, 8 figures available from author
Plasmonics in topological insulators: Spin-charge separation, the influence of the inversion layer, and phonon-plasmon coupling
We demonstrate via three examples that topological insulators (TI) offer a
new platform for plasmonics. First, we show that the collective excitations of
a thin slab of a TI display spin-charge separation. This gives rise to purely
charge-like optical and purely spin-like acoustic plasmons, respectively.
Second, we argue that the depletion layer mixes Dirac and Schr\"odinger
electrons which can lead to novel features such as high modulation depths and
interband plasmons. The analysis is based on an extension of the usual formula
for optical plasmons that depends on the slab width and on the dielectric
constant of the TI. Third, we discuss the coupling of the TI surface phonons to
the plasmons and find strong hybridisation especially for samples with large
slab widths.Comment: 37 pages, 7 figure
Spin-charge separation of plasmonic excitations in thin topological insulators
We discuss plasmonic excitations in a thin slab of a topological insulators.
In the limit of no hybridization of the surface states and same electronic
density of the two layers, the electrostatic coupling between the top and
bottom layers leads to optical and acoustic plasmons which are purely charge
and spin collective oscillations. We then argue that a recent experiment on the
plasmonic excitations of Bi2Se3 [Di Pietro et al, Nat. Nanotechnol. 8, 556
(2013)] must be explained by including the charge response of the
two-dimensional electron gas of the depletion layer underneath the two
surfaces. We also present an analytic formula to fit their data.Comment: 7 pages, 5 figure
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