323 research outputs found
Selective excitation of plasmons superlocalized at sharp perturbations of metal nanoparticles
Sharp metal corners and tips support plasmons localized on the scale of the
curvature radius -- superlocalized plasmons. We analyze plasmonic properties of
nanoparticles with small and sharp corner- and tip-shaped surface perturbations
in terms of hybridization of the superlocalized plasmons, which frequencies are
determined by the perturbations shape, and the ordinary plasmons localized on
the whole particle. When the frequency of a superlocalized plasmon gets close
to that of the ordinary plasmon, their strong hybridization occurs and
facilitates excitation of an optical hot-spot near the corresponding
perturbation apex. The particle is then employed as a nano-antenna that
selectively couples the free-space light to the nanoscale vicinity of the apex
providing precise local light enhancement by several orders of magnitude
Asymmetry in shape causing absolute negative mobility
We propose a simple classical concept of nanodevices working in an absolute
negative mobility (ANM) regime: The minimal spatial asymmetry required for ANM
to occur is embedded in the geometry of the transported particle, rather than
in the channel design. This allows for a tremendous simplification of device
engineering, thus paving the way towards practical implementations of ANM.
Operating conditions and performance of our model device are investigated, both
numerically and analytically.Comment: 6 pages; accepted for publication in PR
Probing Pauli Blocking Factors in Quantum Pumps with Broken Time-Reversal Symmetry
A recently demonstrated quantum electron pump is discussed within the
framework of photon-assisted tunneling. Due to lack of time-reversal symmetry,
different results are obtained for the pump current depending on whether or not
final-state Pauli blocking factors are used when describing the tunneling
process. Whilst in both cases the current depends quadratically on the driving
amplitude for moderate pumping, a marked difference is predicted for the
temperature dependence. With blocking factors the pump current decreases
roughly linearly with temperature until k_B T ~ \hbar\omega is reached, whereas
without them it is unaffected by temperature, indicating that the entire Fermi
sea participates in the electronic transport.Comment: 4 pages in RevTex4 (beta4), 6 figures; status: to appear in PR
Highly tunable low-threshold optical parametric oscillation in radially poled whispering gallery resonators
Whispering gallery resonators (WGR's), based on total internal reflection,
possess high quality factors in a broad spectral range. Thus, nonlinear optical
processes in such cavities are ideally suited for the generation of broadband
or tunable electromagnetic radiation. Experimentally and theoretically, we
investigate the tunability of optical parametric oscillation in a radially
structured WGR made of lithium niobate. With a 1.04 /mum pump wave, the signal
and idler waves are tuned from 1.78 to 2.5 \mum - including the point of
degeneracy - by varying the temperature between 20 and 62 {\deg}C. A weak
off-centering of the radial domain structure extends considerably the tuning
capabilities. The oscillation threshold lies in the mW-power range.Comment: 4 pages, 5 figure
Direct current driven by ac electric field in quantum wells
It is shown that the excitation of charge carriers by ac electric field with
zero average driving leads to a direct electric current in quantum well
structures. The current emerges for both linear and circular polarization of
the ac electric field and depends on the field polarization and frequency. We
present a micoscopic model and an analytical theory of such a nonlinear
electron transport in quantum wells with structure inversion asymmetry. In such
systems, dc current is induced by ac electric field which has both the in-plane
and out-of-plane components. The ac field polarized in the interface plane
gives rise to a direct current if the quantum well is subjected to an in-plane
static magnetic field.Comment: 6 pages, 3 figure
First principles calculations of the Shift Current Bulk Photovoltaic Effect in Ferroelectrics
We calculate the bulk photovoltaic response of the ferroelectrics BaTiO
and PbTiO from first principles by applying "shift current" theory to the
electronic structure from density functional theory. The first principles
results for BaTiO reproduce eperimental photocurrent direction and
magnitude as a function of light frequency, as well as the dependence of
current on light polarization, demonstrating that shift current is the dominant
mechanism of the bulk photovoltaic effect in BaTiO. Additionally, we
analyze the relationship between response and material properties in detail.
The photocurrent does not depend simply or strongly on the magnitude of
material polarization, as has been previously assumed; instead, electronic
states with delocalized, covalent bonding that is highly asymmetric along the
current direction are required for strong shift current enhancements. The
complexity of the response dependence on both external and material parameters
suggests applications not only in solar energy conversion, but to
photocatalysis and sensor and switch type devices as well.Comment: First submitted April 2011, submitted PRL July 201
Maxwell-Drude-Bloch dissipative few-cycle optical solitons
We study the propagation of few-cycle pulses in two-component medium
consisting of nonlinear amplifying and absorbing two-level centers embedded
into a linear and conductive host material. First we present a linear theory of
propagation of short pulses in a purely conductive material, and demonstrate
the diffusive behavior for the evolution of the low-frequency components of the
magnetic field in the case of relatively strong conductivity. Then, numerical
simulations carried out in the frame of the full nonlinear theory involving the
Maxwell-Drude-Bloch model reveal the stable creation and propagation of
few-cycle dissipative solitons under excitation by incident femtosecond optical
pulses of relatively high energies. The broadband losses that are introduced by
the medium conductivity represent the main stabilization mechanism for the
dissipative few-cycle solitons.Comment: 38 pages, 10 figures. submitted to Physical Review
Signature of the electron-electron interaction in the magnetic field dependence of nonlinear I-V characteristics in mesoscopic systems
We show that the nonlinear I-V characteristics of mesoscopic samples with
metallic conductivity should contain parts which are linear in the magnetic
field and quadratic in the electric field. These contributions to the current
are entirely due to the electron-electron interaction and consequently they are
proportional to the electron-electron interaction constant. We also note that
both the amplitude and the sign of the current exhibit random oscillations as a
function of temperature
Investigation of photorefractive subharmonics in the absence of wavemixing
Using a new optical configuration free from the influence of photorefractive optical nonlinearity, we investigate the main characteristics of the spatial subharmonic K/2 excited in a Bi12SiO20 crystal by a light-intensity pattern with wave vector K and frequency O. It is shown that in a large region of intensity and applied electric field the optimum value O of the frequency corresponds to the conditions of parametric excitation of the weakly damped eigenmodes of the medium: the space-charge waves. The threshold and above-threshold characteristics of the subharmonic regime are in good agreement with the theory
Asymmetry of Nonlinear Transport and Electron Interactions in Quantum Dots
The symmetry properties of transport beyond the linear regime in chaotic
quantum dots are investigated experimentally. A component of differential
conductance that is antisymmetric in both applied source-drain bias V and
magnetic field B, absent in linear transport, is found to exhibit mesoscopic
fluctuations around a zero average. Typical values of this component allow a
measurement of the electron interaction strength.Comment: related papers at http://marcuslab.harvard.ed
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