273 research outputs found
Stimulated plasmon polariton scattering
The plasmon and phonon polaritons of two-dimensional (2d) and van-der-Waals
materials have recently gained substantial interest. Unfortunately, they are
notoriously hard to observe in linear response because of their strong
confinement, low frequency and longitudinal mode symmetry. Here, we propose a
fundamentally new approach of harnessing nonlinear resonant scattering that we
call stimulated plasmon polariton scattering (SPPS) in analogy to the
opto-acoustic stimulated Brillouin scattering (SBS). We show that SPS allows to
excite, amplify and detect 2d plasmon and phonon polaritons all across the
THz-range while requiring only optical components in the near-IR or visible
range. We present a coupled-mode theory framework for SPS and based on this
find that SPS power gains exceed the very top gains observed in on-chip SBS by
at least an order of magnitude. This opens exciting new possibilities to
fundamental studies of 2d materials and will help closing the THz gap in
spectrocopy and information technology.Comment: 7 pages, 3 figure
Plasmonics for emerging quantum technologies
Expanding the frontiers of information processing technologies and, in
particular, computing with ever increasing speed and capacity has long been
recognized an important societal challenge, calling for the development of the
next generation of quantum technologies. With its potential to exponentially
increase computing power, quantum computing opens up possibilities to carry out
calculations that ordinary computers could not finish in the lifetime of the
Universe, while optical communications based on quantum cryptography become
completely secure. At the same time, the emergence of Big Data and the ever
increasing demands of miniaturization and energy saving technologies bring
about additional fundamental problems and technological challenges to be
addressed in scientific disciplines dealing with light-matter interactions. In
this context, quantum plasmonics represents one of the most promising and
fundamental research directions and, indeed, the only one that enables ultimate
miniaturization of photonic components for quantum optics when being taken to
extreme limits in light-matter interactions.Comment: To appear in Nanophotonic
How nonlocal damping reduces plasmon-enhanced fluorescence in ultranarrow gaps
The nonclassical modification of plasmon-assisted fluorescence enhancement is
theoretically explored by placing two-level dipole emitters at the narrow gaps
encountered in canonical plasmonic architectures, namely dimers and trimers of
different metallic nanoparticles. Through detailed simulations, in comparison
with appropriate analytical modelling, it is shown that within classical
electrodynamics, and for the reduced separations explored here, fluorescence
enhancement factors of the order of can be achieved, with a divergent
behaviour as the particle touching regime is approached. This remarkable
prediction is mainly governed by the dramatic increase in excitation rate
triggered by the corresponding field enhancement inside the gaps. Nevertheless,
once nonclassical corrections are included, the amplification factors decrease
by up to two orders of magnitude and a saturation regime for narrower gaps is
reached. These nonclassical limitations are demonstrated by simulations based
on the generalised nonlocal optical response theory, which accounts in an
efficient way not only for nonlocal screening, but also for the enhanced Landau
damping near the metal surface. A simple strategy to introduce nonlocal
corrections to the analytic solutions is also proposed. It is therefore shown
that the nonlocal optical response of the metal imposes more realistic, finite
upper bounds to the enhancement feasible with ultrasmall plasmonic cavities,
thus providing a theoretical description closer to state of the art
experiments
Enhanced ponderomotive force in graphene due to interband resonance
We analyze intrinsic nonlinearities in two-dimensional polaritonic materials
interacting with an optical wave. Focusing on the case of graphene, we show
that the second-order nonlinear optical conductivity due to carrier density
fluctuations associated with the excitation of a plasmon polariton is closely
related to the ponderomotive force due to the oscillating optical field. This
relation is first established through an elegant thermodynamic approach for a
Drude-like plasma, in the frequency range where intraband scattering is the
dominant contribution to conductivity. Subsequently, we extend our analysis to
the interband regime, and show that for energies approximately half the Fermi
energy, the intraband contribution to the ponderomotive force diverges. In
practice, thermal broadening regularizes this divergence as one would expect,
but even at room temperature typically leaves a strong ponderomotive
enhancement. Finally, we study the impact of nonlocal corrections and find that
nonlocality does not lead to further broadening (as one would expect in the
case of Landau damping), but rather to a splitting of the ponderomotive
interband resonance. Our analysis should prove useful to the open quest for
exploiting nonlinearities in graphene and other two-dimensional polaritonic
materials, through effects such as second harmonic generation and photon drag.Comment: 7 pages, 2 figures, 1 appendi
Robustness of the Rabi splitting under nonlocal corrections in plexcitonics
We explore theoretically how nonlocal corrections in the description of the
metal affect the strong coupling between excitons and plasmons in typical
examples where nonlocal effects are anticipated to be strong, namely small
metallic nanoparticles, thin metallic nanoshells or dimers with narrow
separations, either coated with or encapsulating an excitonic layer. Through
detailed simulations based on the generalised nonlocal optical response theory,
which simultaneously accounts both for modal shifts due to screening and for
surface-enhanced Landau damping, we show that, contrary to expectations, the
influence of nonlocality is rather limited, as in most occasions the width of
the Rabi splitting remains largely unaffected and the two hybrid modes are well
distinguishable. We discuss how this behaviour can be understood in view of the
popular coupled-harmonic-oscillator model, while we also provide analytic
solutions based on Mie theory to describe the hybrid modes in the case of
matryoshka-like single nanoparticles. Our analysis provides an answer to a so
far open question, that of the influence of nonlocality on strong coupling, and
is expected to facilitate the design and study of plexcitonic architectures
with ultrafine geometrical details
Projected-Dipole Model for Quantum Plasmonics
Quantum effects of plasmonic phenomena have been explored through ab-initio
studies, but only for exceedingly small metallic nanostructures, leaving most
experimentally relevant structures too large to handle. We propose instead an
effective description with the computationally appealing features of classical
electrodynamics, while quantum properties are described accurately through an
infinitely thin layer of dipoles oriented normally to the metal surface. The
nonlocal polarizability of the dipole layer is mapped from the free-electron
distribution near the metal surface as obtained with 1D quantum calculations,
such as time-dependent density-functional theory (TDDFT), and is determined
once and for all. The model can be applied to any system size that is tractable
within classical electrodynamics, while capturing quantum plasmonic aspects of
nonlocal response and a finite work function with TDDFT-level accuracy.
Applying the theory to dimers we find quantum-corrections to the hybridization
even in mesoscopic dimers as long as the gap is sub-nanometric itself.Comment: Supplemental Material is available upon request to author
Localized plasmons in bilayer graphene nanodisks
We study localized plasmonic excitations in bilayer graphene (BLG) nanodisks,
comparing AA-stacked and AB-stacked BLG and contrasting the results to the case
of two monolayers without electronic hybridization. The electrodynamic response
of the BLG electron gas is described in terms of a spatially homogeneous
surface conductivity, and an efficient alternative two-dimensional
electrostatic approach is employed to carry out all the numerical calculations
of plasmon resonances. Due to a unique electronic band structures, the
resonance frequency of the traditional dipolar plasmonic mode in the AA-stacked
BLG nanodisk is roughly doping independent in the low-doping regime, while the
mode is highly damped as the Fermi level approaches the interlayer hopping
energy associated with tunneling of electrons between the two layers.
In addition to the traditional dipolar mode, we find that the AB-stacked BLG
nanodisk also hosts a new plasmonic mode with energy larger than . This
mode can be tuned by either the doping level or structural size, and
furthermore, this mode can dominate the plasmonic response for realistic
structural conditions
Two-fluid hydrodynamic model for semiconductors
The hydrodynamic Drude model (HDM) has been successful in describing the
optical properties of metallic nanostructures, but for semiconductors where
several different kinds of charge carriers are present, an extended theory is
required. We present a two-fluid hydrodynamic model for semiconductors
containing electrons and holes (from thermal or external excitation) or light
and heavy holes (in -doped materials). The two-fluid model predicts the
existence of two longitudinal modes, an acoustic and an optical, whereas only
an optical mode is present in the HDM. By extending nonlocal Mie theory to two
plasmas, we are able to simulate the optical properties of two-fluid
nanospheres and predict that the acoustic mode gives rise to peaks in the
extinction spectra that are absent in the HDM.Comment: Accepted in PRB. 17 pages, 9 figures, 1 tabl
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