778 research outputs found
Semiconductor-metal nanoparticle molecules: hybrid excitons and non-linear Fano effect
Modern nanotechnology opens the possibility of combining nanocrystals of
various materials with very different characteristics in one superstructure.
The resultant superstructure may provide new physical properties not
encountered in homogeneous systems. Here we study theoretically the optical
properties of hybrid molecules composed of semiconductor and metal
nanoparticles. Excitons and plasmons in such a hybrid molecule become strongly
coupled and demonstrate novel properties. At low incident light intensity, the
exciton peak in the absorption spectrum is broadened and shifted due to
incoherent and coherent interactions between metal and semiconductor
nanoparticles. At high light intensity, the absorption spectrum demonstrates a
surprising, strongly asymmetric shape. This shape originates from the coherent
inter-nanoparticle Coulomb interaction and can be viewed as a non-linear Fano
effect which is quite different from the usual linear Fano resonance.Comment: 5 pages, 5 figures, submitted to Phys. Rev. Let
Giant Modal Gain, Amplified Surface Plasmon Polariton Propagation, and Slowing Down of Energy Velocity in a Metal-Semiconductor-Metal Structure
We investigated surface plasmon polariton (SPP) propagation in a
metal-semiconductor-metal structure where semiconductor is highly excited to
have optical gain. We show that near the SPP resonance, the imaginary part of
the propagation wavevector changes from positive to hugely negative,
corresponding to an amplified SPP propagation. The SPP experiences a giant gain
that is 1000 times of material gain in the excited semiconductor. We show that
such a giant gain is related to the slowing down of average energy propagation
in the structur
Direct Measurement of intermediate-range Casimir-Polder potentials
We present the first direct measurements of Casimir-Polder forces between
solid surfaces and atomic gases in the transition regime between the
electrostatic short-distance and the retarded long-distance limit. The
experimental method is based on ultracold ground-state Rb atoms that are
reflected from evanescent wave barriers at the surface of a dielectric glass
prism. Our novel approach does not require assumptions about the potential
shape. The experimental data confirm the theoretical prediction in the
transition regime.Comment: 4 pages, 3 figure
One-electron states and interband optical absorption in single-wall carbon nanotubes
Explicit expressions for the wave functions and dispersion equation for the
band p - electrons in single-wall carbon nanotubes are obtained within the
method of zero-range potentials. They are then used to investigate the
absorption spectrum of polarized light caused by direct interband transitions
in isolated nanotubes. It is shown that, at least, under the above
approximations, the circular dichroism is absent in chiral nanotubes for the
light wave propagating along the tube axis. The results obtained are compared
with those calculated in a similar way for a graphite plane.Comment: 16 pages, 8 figures, 1 tabl
Phase-change chalcogenide glass metamaterial
Combining metamaterials with functional media brings a new dimension to their
performance. Here we demonstrate substantial resonance frequency tuning in a
photonic metamaterial hybridized with an electrically/optically switchable
chalcogenide glass. The transition between amorphous and crystalline forms
brings about a 10% shift in the near-infrared resonance wavelength of an
asymmetric split-ring array, providing transmission modulation functionality
with a contrast ratio of 4:1 in a device of sub-wavelength thickness.Comment: 3 pages, 3 figure
Optical detection of spin transport in non-magnetic metals
We determine the dynamic magnetization induced in non-magnetic metal wedges
composed of silver, copper and platinum by means of Brillouin light scattering
(BLS) microscopy. The magnetization is transferred from a ferromagnetic
Ni80Fe20 layer to the metal wedge via the spin pumping effect. The spin pumping
efficiency can be controlled by adding an insulating but transparent interlayer
between the magnetic and non-magnetic layer. By comparing the experimental
results to a dynamical macroscopic spin-transport model we determine the
transverse relaxation time of the pumped spin current which is much smaller
than the longitudinal relaxation time
Exact microscopic theory of electromagnetic heat transfer between a dielectric sphere and plate
Near-field electromagnetic heat transfer holds great potential for the
advancement of nanotechnology. Whereas far-field electromagnetic heat transfer
is constrained by Planck's blackbody limit, the increased density of states in
the near-field enhances heat transfer rates by orders of magnitude relative to
the conventional limit. Such enhancement opens new possibilities in numerous
applications, including thermal-photo-voltaics, nano-patterning, and imaging.
The advancement in this area, however, has been hampered by the lack of
rigorous theoretical treatment, especially for geometries that are of direct
experimental relevance. Here we introduce an efficient computational strategy,
and present the first rigorous calculation of electromagnetic heat transfer in
a sphere-plate geometry, the only geometry where transfer rate beyond blackbody
limit has been quantitatively probed at room temperature. Our approach results
in a definitive picture unifying various approximations previously used to
treat this problem, and provides new physical insights for designing
experiments aiming to explore enhanced thermal transfer.Comment: 1 page title 8 page content 1 page references 2 page figure captions
4 page figure
Resonant absorption of electromagnetic fields by surface plasmons buried in a multilayered plasmonic nanostructure
Alastair P. Hibbins, W. Andrew Murray, J. Tyler, S. Wedge, William L. Barnes, and J. Roy Sambles, Physical Review B, Vol. 74, article 073408 (2006). "Copyright © 2006 by the American Physical Society."The optical reflectivity of a metal-dielectric-metal microcavity in which the upper layer is periodically perforated by narrow slits is explored. Complete characterization of the observed modes in terms of their resonant electromagnetic fields is achieved by comparison of the experimental data to the predictions of a finite-element model. In particular, we demonstrate that the slits provide efficient diffractive coupling to a surface plasmon mode buried within the microcavity whose propagation is strongly confined to the dielectric layer
Dual-tip-enhanced ultrafast CARS nanoscopy
Coherent anti-Stokes Raman scattering (CARS) and, in particular, femtosecond
adaptive spectroscopic techniques (FAST CARS) have been successfully used for
molecular spectroscopy and microscopic imaging. Recent progress in ultrafast
nanooptics provides flexibility in generation and control of optical near
fields, and holds promise to extend CARS techniques to the nanoscale. In this
theoretical study, we demonstrate ultrafast subwavelentgh control of coherent
Raman spectra of molecules in the vicinity of a plasmonic nanostructure excited
by ultrashort laser pulses. The simulated nanostructure design provides
localized excitation sources for CARS by focusing incident laser pulses into
subwavelength hot spots via two self-similar nanolens antennas connected by a
waveguide. Hot-spot-selective dual-tip-enhanced CARS (2TECARS) nanospectra of
DNA nucleobases are obtained by simulating optimized pump, Stokes and probe
near fields using tips, laser polarization- and pulse-shaping. This technique
may be used to explore ultrafast energy and electron transfer dynamics in real
space with nanometre resolution and to develop novel approaches to DNA
sequencing.Comment: 11 pages, 6 figure
Casimir Force between a Dielectric Sphere and a Wall: A Model for Amplification of Vacuum Fluctuations
The interaction between a polarizable particle and a reflecting wall is
examined. A macroscopic approach is adopted in which the averaged force is
computed from the Maxwell stress tensor. The particular case of a perfectly
reflecting wall and a sphere with a dielectric function given by the Drude
model is examined in detail. It is found that the force can be expressed as the
sum of a monotonically decaying function of position and of an oscillatory
piece. At large separations, the oscillatory piece is the dominant
contribution, and is much larger than the Casimir-Polder interaction that
arises in the limit that the sphere is a perfect conductor. It is argued that
this enhancement of the force can be interpreted in terms of the frequency
spectrum of vacuum fluctuations. In the limit of a perfectly conducting sphere,
there are cancellations between different parts of the spectrum which no longer
occur as completely in the case of a sphere with frequency dependent
polarizability. Estimates of the magnitude of the oscillatory component of the
force suggest that it may be large enough to be observable.Comment: 18pp, LaTex, 7 figures, uses epsf. Several minor errors corrected,
additional comments added in the final two sections, and references update
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