8,032 research outputs found
Switching from visibility to invisibility via Fano resonances: theory and experiment
Subwavelength structures demonstrate many unusual optical properties which
can be employed for engineering functional metadevices, as well as scattering
of light and invisibility cloaking. Here we demonstrate that the suppression of
light scattering for any direction of observation can be achieved for an
uniform dielectric object with high refractive index, in a sharp contrast to
the cloaking with multilayered plasmonic structures suggested previously. Our
finding is based on the novel physics of cascades of Fano resonances observed
in the Mie scattering from a homogeneous dielectric rod. We observe this effect
experimentally at microwaves by employing high temperature-dependent dielectric
permittivity of a glass cylinder with heated water. Our results open a new
avenue in analyzing the optical response of hight-index dielectric
nanoparticles and the physics of cloaking.Comment: 8 pages, 4 figure
Non-abelian 4-d black holes, wrapped 5-branes, and their dual descriptions
We study extremal and non-extremal generalizations of the regular non-abelian
monopole solution of hep-th/9707176, interpreted in hep-th/0007018 as 5-branes
wrapped on a shrinking S^2. Naively, the low energy dynamics is pure N=1
supersymmetric Yang-Mills. However, our results suggest that the scale of
confinement and chiral symmetry breaking in the Yang-Mills theory actually
coincides with the Hagedorn temperature of the little string theory. We find
solutions with regular horizons and arbitrarily high Hawking temperature.
Chiral symmetry is restored at high energy density, corresponding to large
black holes. But the entropy of the black hole solutions decreases as one
proceeds to higher temperatures, indicating that there is a thermodynamic
instability and that the canonical ensemble is ill-defined. For certain limits
of the black hole solutions, we exhibit explicit non-linear sigma models
involving a linear dilaton. In other limits we find extremal non-BPS solutions
which may have some relevance to string cosmology.Comment: 53 pages, 21 figures, latex. v2: slightly improved figure
Bosonized supersymmetry from the Majorana-Dirac-Staunton theory and massive higher-spin fields
We propose a (3+1)D linear set of covariant vector equations, which unify the
spin 0 ``new Dirac equation'' with its spin 1/2 counterpart, proposed by
Staunton. Our equations describe a spin (0,1/2) supermultiplet with different
numbers of degrees of freedom in the bosonic and fermionic sectors. The
translation-invariant spin deegres of freedom are carried by two copies of the
Heisenberg algebra. This allows us to realize space-time supersymmetry in a
bosonized form. The grading structure is provided by an internal reflection
operator. Then the construction is generalized by means of the Majorana
equation to a supersymmetric theory of massive higher-spin particles. The
resulting theory is characterized by a nonlinear symmetry superalgebra, that,
in the large-spin limit, reduces to the super-Poincare algebra with or without
tensorial central charge.Comment: 21 pages; refs added, version accepted for publication in Physical
Review
Supersymmetry between Jackiw-Nair and Dirac-Majorana anyons
The Jackiw-Nair description of anyons combines spin-1 topologically massive
fields with the discrete series representation of the Lorentz algebra, which
has fractional spin. In the Dirac-Majorana formulation the spin-1 part is
replaced by the spin 1/2 planar Dirac equation. The two models are shown to
belong to an N=1 supermultiplet, which carries a super-Poincare symmetry.Comment: 4 pages, no figures. Typos corrected. Published versio
Phase diagram for the transition from photonic crystals to dielectric metamaterials
Photonic crystals and metamaterials represent two seemingly different classes
of artificial electromagnetic media but often they are composed of similar
structural elements arranged in periodic lattices. The important question is
how to distinguish these two types of periodic photonic structures when their
parameters, such as dielectric permittivity and lattice spacing, vary
continuously. Here, we discuss transitions between photonic crystals and
all-dielectric metamaterials and introduce the concept of a phase diagram and
an order parameter for such structured materials, based on the physics of Mie
and Bragg resonances. We show that a periodic photonic structure transforms
into a metamaterial when the Mie gap opens up below the lowest Bragg bandgap
where the homogenization approach can be justified and the effective
permeability becomes negative. Our theoretical approach is confirmed by
detailed microwave experiments for a metacrystal composed of a square lattice
of glass tubes filled with heated water. This analysis yields deep insight into
the properties of periodic photonic structures, and it also provides a useful
tool for designing different classes of electromagnetic materials in a broad
range of parameters.Comment: 7 pages, 6 figure
Evidence for Kinetic Limitations as a Controlling Factor of Ge Pyramid Formation: a Study of Structural Features of Ge/Si(001) Wetting Layer Formed by Ge Deposition at Room Temperature Followed by Annealing at 600 {\deg}C
The article presents an experimental study of an issue of whether the
formation of arrays of Ge quantum dots on the Si(001) surface is an equilibrium
process or it is kinetically controlled. We deposited Ge on Si(001) at the room
temperature and explored crystallization of the disordered Ge film as a result
of annealing at 600 {\deg}C. The experiment has demonstrated that the
Ge/Si(001) film formed in the conditions of an isolated system consists of the
standard patched wetting layer and large droplike clusters of Ge rather than of
huts or domes which appear when a film is grown in a flux of Ge atoms arriving
on its surface. We conclude that the growth of the pyramids appearing at
temperatures greater than 600 {\deg}C is controlled by kinetics rather than
thermodynamic equilibrium whereas the wetting layer is an equilibrium
structure.Comment: Accepted for publication in Nanoscale Research Letter
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