634 research outputs found
Non-equilibrium electromagnetic fluctuations: Heat transfer and interactions
The Casimir force between arbitrary objects in equilibrium is related to
scattering from individual bodies. We extend this approach to heat transfer and
Casimir forces in non-equilibrium cases where each body, and the environment,
is at a different temperature. The formalism tracks the radiation from each
body and its scatterings by the other objects. We discuss the radiation from a
cylinder, emphasizing its polarized nature, and obtain the heat transfer
between a sphere and a plate, demonstrating the validity of proximity transfer
approximation at close separations and arbitrary temperatures.Comment: 4 pages, 2 figures, published version, minor changes (e.g. typos
Strong absorption and selective thermal emission from a mid-infrared metamaterial
We demonstrate thin-film metamaterials with resonances in the mid-infrared
wavelength range. Our structures are numerically modeled and experimentally
characterized by reflection and angularly-resolved thermal emission
spectroscopy. We demonstrate strong and controllable absorption resonances
across the mid-infrared wavelength range. In addition, the polarized thermal
emission from these samples is shown to be highly selective and largely
independent of emission angles from normal to 45 degrees. Experimental results
are compared to numerical models with excellent agreement. Such structures hold
promise for large-area, low-cost metamaterial coatings for control of gray- or
black-body thermal signatures, as well as for possible mid-IR sensing
applications.Comment: The following article has been submitted to Appl. Phys. Lett. After
it is published, it will be found at http://apl.aip.org/. 14 pages including
4 figure page
Fundamental limits for non-contact transfers between two bodies
We investigate energy and momentum non-contact exchanges between two
arbitrary flat media separated by a gap. This problem is revisited as a
transmission problem of individual system eigenmodes weighted by a transmission
probability obtained either from fluctuational electrodynamics or quantum field
theory. An upper limit for energy and momentum flux is derived using a general
variational approach. The corresponding optimal reflectivity coefficients are
given both for identical and different media in interaction.Comment: accepted in Phys. Rev. B rapid communicatio
Phonitons as a sound-based analogue of cavity quantum electrodynamics
A quantum mechanical superposition of a long-lived, localized phonon and a
matter excitation is described. We identify a realization in strained silicon:
a low-lying donor transition (P or Li) driven solely by acoustic phonons at
wavelengths where high-Q phonon cavities can be built. This phonon-matter
resonance is shown to enter the strongly coupled regime where the "vacuum" Rabi
frequency exceeds the spontaneous phonon emission into non-cavity modes, phonon
leakage from the cavity, and phonon anharmonicity and scattering. We introduce
a micropillar distributed Bragg reflector Si/Ge cavity, where Q=10^5-10^6 and
mode volumes V<=25*lambda^3 are reachable. These results indicate that single
or many-body devices based on these systems are experimentally realizable.Comment: Published PRL version. Note that the previous arXiv version has more
commentary, figures, etc. Also see http://research.tahan.com
Phonons in Random Elastic Media and the Boson Peak
We show that the density of states of random wave equations, normalized by
the square of the frequency, has a peak - sometimes narrow and sometimes broad
- in the range of wave vectors between the disorder correlation length and the
interatomic spacing. The results of this letter may be relevant for
understanding vibrational spectra and light propagation in disordered solids
Magnetic noise around metallic microstructures
We compute the local spectrum of the magnetic field near a metallic
microstructure at finite temperature. Our main focus is on deviations from a
plane-layered geometry for which we review the main properties. Arbitrary
geometries are handled with the help of numerical calculations based on surface
integral equations. The magnetic noise shows a significant polarization
anisotropy above flat wires with finite lateral width, in stark contrast to an
infinitely wide wire. Within the limits of a two-dimensional setting, our
results provide accurate estimates for loss and dephasing rates in so-called
`atom chip traps' based on metallic wires. A simple approximation based on the
incoherent summation of local current elements gives qualitative agreement with
the numerics, but fails to describe current correlations among neighboring
objects.Comment: 10 pages, 9 figures, accepted for publication in J Appl Phys; figures
plotted for slightly smaller structur
Generation and remote detection of THz sound using semiconductor superlattices
The authors introduce a novel approach to study the propagation of high
frequency acoustic phonons in which the generation and detection involves two
spatially separated superlattices apart. Propagating modes
of frequencies up to escape from the superlattice where they
are generated and reach the second superlattice where they are detected. The
measured frequency spectrum reveals finite size effects, which can be accounted
for by a continuum elastic model.Comment: Submitted to Applied Physics Letter
A non-destructive analytic tool for nanostructured materials : Raman and photoluminescence spectroscopy
Modern materials science requires efficient processing and characterization
techniques for low dimensional systems. Raman spectroscopy is an important
non-destructive tool, which provides enormous information on these materials.
This understanding is not only interesting in its own right from a physicist's
point of view, but can also be of considerable importance in optoelectronics
and device applications of these materials in nanotechnology. The commercial
Raman spectrometers are quite expensive. In this article, we have presented a
relatively less expensive set-up with home-built collection optics attachment.
The details of the instrumentation have been described. Studies on four classes
of nanostructures - Ge nanoparticles, porous silicon (nanowire), carbon
nanotubes and 2D InGaAs quantum layers, demonstrate that this unit can be of
use in teaching and research on nanomaterials.Comment: 32 pages, 13 figure
Once More About the Possibility of Determining the Local Electron Concentration by the Dispersion Method with the Help of AES and on New Ionization Maxima in the Ionosphere
Reliability of ionospheric density measurements by satellites using dispersion metho
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