2,545 research outputs found
Extraordinary nonlinear plasmonics in graphene nanoislands
Nonlinear optical processes rely on the intrinsically weak interactions
between photons enabled by their coupling with matter. Unfortunately, many
applications in nonlinear optics are severely hindered by the small response of
conventional materials. Metallic nanostructures partially alleviate this
situation, as the large light enhancement associated with their localized
plasmons amplifies their nonlinear response to record high levels. Graphene
hosts long-lived, electrically tunable plasmons that also interact strongly
with light. Here we show that the nonlinear polarizabilities of graphene
nanoislands can be electrically tuned to surpass by several orders of magnitude
those of metal nanoparticles of similar size. This extraordinary behavior
extends over the visible and near-infrared for islands consisting of hundreds
of carbon atoms doped with moderate carrier densities. Our quantum-mechanical
simulations of the plasmon-enhanced optical response of nanographene reveal
this material as an ideal platform for the development of electrically tunable
nonlinear optical nanodevices.Comment: 16 pages, 12 figures, 54 reference
Nonlinear Plasmonic Sensing with Nanographene
Plasmons provide excellent sensitivity to detect analyte molecules through their strong interaction with
the dielectric environment. Plasmonic sensors based on noble metals are, however, limited by the spectral
broadening of these excitations. Here we identify a new mechanism that reveals the presence of individual
molecules through the radical changes that they produce in the plasmons of graphene nanoislands. An
elementary charge or a weak permanent dipole carried by the molecule are shown to be sufficient to trigger
observable modifications in the linear absorption spectra and the nonlinear response of the nanoislands. In
particular, a strong second-harmonic signal, forbidden by symmetry in the unexposed graphene nanostructure,
emerges due to a redistribution of conduction electrons produced by interaction with the
molecule. These results pave the way toward ultrasensitive nonlinear detection of dipolar molecules and
molecular radicals that is made possible by the extraordinary optoelectronic properties of graphene.Peer ReviewedPostprint (published version
Dipole-dipole interaction between a quantum dot and graphene nanodisk
We study theoretically the dipole-dipole interaction and energy transfer in a
hybrid system consisting of a quantum dot and graphene nanodisk embedded in a
nonlinear photonic crystal. In our model a probe laser field is applied to
measure the energy transfer between the quantum dot and graphene nanodisk while
a control field manipulates the energy transfer process. These fields create
excitons in the quantum dot and surface plasmon polaritons in the graphene
nanodisk which interact via the dipole-dipole interaction. Here the nonlinear
photonic crystal acts as a tunable photonic reservoir for the quantum dot, and
is used to control the energy transfer. We have found that the spectrum of
power absorption in the quantum dot has two peaks due to the creation of two
dressed excitons in the presence of the dipole-dipole interaction. The energy
transfer rate spectrum of the graphene nanodisk also has two peaks due to the
absorption of these two dressed excitons. Additionally, energy transfer between
the quantum dot and the graphene nanodisk can be switched on and off by
applying a pump laser to the photonic crystal or by adjusting the strength of
the dipole-dipole interaction. We show that the intensity and frequencies of
the peaks in the energy transfer rate spectra can be modified by changing the
number of graphene monolayers in the nanodisk or the separation between the
quantum dot and graphene. Our results agree with existing experiments on a
qualitative basis. The principle of our system can be employed to fabricate
nano-biosensors, optical nano-switches, and energy transfer devices
An exploration of sex-specific linkage disequilibrium on chromosome X in Caucasians from the COGA study
This paper explores the decay of linkage disequilibrium (LD) on the autosomes and chromosome X. The extent of marker-marker LD is important for both linkage and association studies. The analysis of the Caucasian sample from the Collaborative Study on the Genetics of Alcoholism study revealed the expected negative relationship between the magnitude of the marker-marker LD and distance (cM), with the male and female subgroups exhibiting similar patterns of LD. The observed extent of LD in females was less across the pseudoautosomal markers relative to the heterosomal region of chromosome X. Marked differences in LD patterns were also observed between chromosomes X and the 22 autosomes in both males and females
Plasmons in doped finite carbon nanotubes and their interactions with fast electrons and quantum emitters
We study the potential of highly doped finite carbon nanotubes to serve as plasmonic elements that mediate the interaction between quantum emitters. Similar to graphene, nanotubes support intense plasmons that can be modulated by varying their level of electrical doping. These excitations exhibit large interaction with light and electron beams, as revealed upon examination of the corresponding light extinction cross-section and electron energy-loss spectra. We show that quantum emitters experience record-high Purcell factors, while they undergo strong mutual interaction mediated by their coupling to the tube plasmons. Our results show the potential of doped finite nanotubes as tunable plasmonic materials for quantum optics applicationsPeer ReviewedPostprint (author's final draft
Nonlocal effects in atom-plasmon interactions
Nonlocal and quantum mechanical phenomena in noble metal nanostructures
become increasingly crucial when the relevant length scales in hybrid
nanostructures reach the few-nanometer regime. In practice, such mesoscopic
effects at metal-dielectric interfaces can be described using exemplary
surface-response functions (SRFs) embodied by the Feibelman -parameters.
Here we show that SRFs dramatically influence quantum electrodynamic phenomena
-- such as the Purcell enhancement and Lamb shift -- for quantum emitters close
to a diverse range of noble metal nanostructures interfacing different
homogeneous media. Dielectric environments with higher permittivities are shown
to increase the magnitude of SRFs calculated within the specular-reflection
model. In parallel, the role of SRFs is enhanced in nanostructures
characterized by large surface-to-volume ratios, such as thin planar metallic
films or shells of core-shell nanoparticles. By investigating emitter quantum
dynamics close to such plasmonic architectures, we show that decreasing the
width of the metal region, or increasing the permittivity of the interfacing
dielectric, leads to a significant change in the Purcell enhancement, Lamb
shift, and visible far-field spontaneous emission spectrum, as an immediate
consequence of SRFs. We anticipate that fitting the theoretically modelled
spectra to experiments could allow for experimental determination of the
-parameters.Comment: 9 pages, 5 figure
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