2,492 research outputs found
Magneto-Roton Modes of the Ultra Quantum Crystal: Numerical Study
The Field Induced Spin Density Wave phases observed in quasi-one-dimensional
conductors of the Bechgaard salts family under magnetic field exhibit both Spin
Density Wave order and a Quantized Hall Effect, which may exhibit sign
reversals. The original nature of the condensed phases is evidenced by the
collective mode spectrum. Besides the Goldstone modes, a quasi periodic
structure of Magneto-Roton modes, predicted to exist for a monotonic sequence
of Hall Quantum numbers, is confirmed, and a second mode is shown to exist
within the single particle gap. We present numerical estimates of the
Magneto-Roton mode energies in a generic case of the monotonic sequence. The
mass anisotropy of the collective mode is calculated. We show how differently
the MR spectrum evolves with magnetic field at low and high fields. The
collective mode spectrum should have specific features, in the sign reversed
"Ribault Phase", as compared to modes of the majority sign phases. We
investigate numerically the collective mode in the Ribault Phase.Comment: this paper incorporates material contained in a previous cond-mat
preprint cond-mat/9709210, but cannot be described as a replaced version,
because it contains a significant amount of new material dealing with the
instability line and with the topic of Ribault Phases. It contains 13 figures
(.ps files
Cloaking dielectric spherical objects by a shell of metallic nanoparticles
We show that dielectric spheres can be cloaked by a shell of amorphously
arranged metallic nanoparticles. The shell represents an artificial medium with
tunable effective properties that can be adjusted such that the scattered
signals of shell and sphere almost cancel each other. We provide an analytical
model for the cloak design and prove numerically that the cloak operates as
desired. We show that more than 70% of the scattered signal of the sphere can
be suppressed at the design wavelength. Advantages and disadvantages of such a
cloak when compared to other implementations are disclosed.Comment: 14 pages, 6 figure
An alternative search for the electron capture of Te-123
A search for the electron capture of Te-123 has been performed using CdZnTe
detectors. After a measuring time of 195 h no signal could be found resulting
in a lower half-life limt of yrs (95 % CL) for
this process. This clearly discriminates between existing experimental results
which differ by six orders of magnitude and our data are in strong favour of
the result with longer half-lifes.Comment: 2 pages, 2 eps-figures, reanalysis of data set
Validity of effective material parameters for optical fishnet metamaterials
Although optical metamaterials that show artificial magnetism are mesoscopic
systems, they are frequently described in terms of effective material
parameters. But due to intrinsic nonlocal (or spatially dispersive) effects it
may be anticipated that this approach is usually only a crude approximation and
is physically meaningless. In order to study the limitations regarding the
assignment of effective material parameters, we present a technique to retrieve
the frequency-dependent elements of the effective permittivity and permeability
tensors for arbitrary angles of incidence and apply the method exemplarily to
the fishnet metamaterial. It turns out that for the fishnet metamaterial,
genuine effective material parameters can only be introduced if quite stringent
constraints are imposed on the wavelength/unit cell size ratio. Unfortunately
they are only met far away from the resonances that induce a magnetic response
required for many envisioned applications of such a fishnet metamaterial. Our
work clearly indicates that the mesoscopic nature and the related spatial
dispersion of contemporary optical metamaterials that show artificial magnetism
prohibits the meaningful introduction of conventional effective material
parameters
Doubly resonant optical nanoantenna arrays for polarization resolved measurements of surface-enhanced Raman scattering
We report that rhomb-shaped metal nanoantenna arrays support multiple
plasmonic resonances, making them favorable bio-sensing substrates. Besides the
two localized plasmonic dipole modes associated with the two principle axes of
the rhombi, the sample supports an additional grating-induced surface plasmon
polariton resonance. The plasmonic properties of all modes are carefully
studied by far-field measurements together with numerical and analytical
calculations. The sample is then applied to surface-enhanced Raman scattering
measurements. It is shown to be highly efficient since two plasmonic resonances
of the structure were simultaneously tuned to coincide with the excitation and
the emission wave- length in the SERS experiment. The analysis is completed by
measuring the impact of the polarization angle on the SERS signal.Comment: 13 pages, 5 figure
Circular Optical Nanoantennas: An Analytical Theory
An entirely analytical theory is provided for describing the resonance
properties of optical nanoantennas made of a stack of homogeneous discs, i.e.
circular patch nanoantennas. It consists in analytically calculating the phase
accumulation of surface plasmon polaritons across the resonator and an
additional contribution from the complex reflection coefficient at the antenna
termination. This makes the theory self-contained with no need for fitting
parameters. The very antenna resonances are then explained by a simple
Fabry-Perot resonator model. Predictions are compared to rigorous simulations
and show excellent agreement. Using this analytical model, circular antennas
can be tuned by varying the composition of the stack
d-wave superconductivity and Pomeranchuk instability in the two-dimensional Hubbard model
We present a systematic stability analysis for the two-dimensional Hubbard
model, which is based on a new renormalization group method for interacting
Fermi systems. The flow of effective interactions and susceptibilities confirms
the expected existence of a d-wave pairing instability driven by
antiferromagnetic spin fluctuations. More unexpectedly, we find that strong
forward scattering interactions develop which may lead to a Pomeranchuk
instability breaking the tetragonal symmetry of the Fermi surface.Comment: 4 pages (RevTeX), 4 eps figure
Wave Function of a Brane-like Universe
Within the mini-superspace model, brane-like cosmology means performing the
variation with respect to the embedding (Minkowski) time before fixing
the cosmic (Einstein) time . The departure from Einstein limit is
parameterized by the 'energy' conjugate to , and characterized by a
classically disconnected Embryonic epoch. In contrast with canonical quantum
gravity, the wave-function of the brane-like Universe is (i) -dependent,
and (ii) vanishes at the Big Bang. Hartle-Hawking and Linde proposals dictate
discrete 'energy' levels, whereas Vilenkin proposal resembles -particle
disintegration.Comment: Revtex, 4 twocolumn pages, 3 eps figures (accepted for publication in
Class. Quan. Grav.
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