44 research outputs found
Plasmon Generation through Electron Tunneling in Graphene
The short wavelength of graphene plasmons relative to the light wavelength
makes them attractive for applications in optoelectronics and sensing. However,
this property limits their coupling to external light and our ability to create
and detect them. More efficient ways of generating plasmons are therefore
desirable. Here we demonstrate through realistic theoretical simulations that
graphene plasmons can be efficiently excited via electron tunneling in a
sandwich structure formed by two graphene monolayers separated by a few atomic
layers of hBN. We obtain plasmon generation rates of s
over an area of the squared plasmon wavelength for realistic values of the
spacing and bias voltage, while the yield (plasmons per tunneled electron) has
unity order. Our results support electrical excitation of graphene plasmons in
tunneling devices as a viable mechanism for the development of optics-free
ultrathin plasmonic devices.Comment: 15 pages, 11 figures, 92 reference
Plasmonics in Atomically Thin Materials
The observation and electrical manipulation of infrared surface plasmons in
graphene have triggered a search for similar photonic capabilities in other
atomically thin materials that enable electrical modulation of light at visible
and near-infrared frequencies, as well as strong interaction with optical
quantum emitters. Here, we present a simple analytical description of the
optical response of such kinds of structures, which we exploit to investigate
their application to light modulation and quantum optics. Specifically, we show
that plasmons in one-atom-thick noble-metal layers can be used both to produce
complete tunable optical absorption and to reach the strong-coupling regime in
the interaction with neighboring quantum emitters. Our methods are applicable
to any plasmon-supporting thin materials, and in particular, we provide
parameters that allow us to readily calculate the response of silver, gold, and
graphene islands. Besides their interest for nanoscale electro-optics, the
present study emphasizes the great potential of these structures for the design
of quantum nanophotonics devices.Comment: 15 pages, 5 figures, 107 ref
Chiral Light Emission from a Sphere Revealed by Nanoscale Relative Phase Mapping
Circularly polarized light (CPL) is currently receiving much attention as a
key ingredient for next-generation information technologies, such as quantum
communication and encryption. CPL photon generation for such applications is
commonly realized by coupling achiral optical quantum emitters to chiral
nanoantennas. Here, we explore a different strategy consisting in exciting a
nanosphere -- the ultimate symmetric structure -- to produce all-directional
CPL emission. Specifically, we demonstrate chiral emission from a silicon
nanosphere induced by an electron beam based on two different strategies:
dissolving the degeneracy of orthogonal dipole modes, and interference of
electric and magnetic modes. We prove these concepts by visualizing the phase
and polarization using a newly developed polarimetric four-dimensional
cathodoluminescence method. Besides their fundamental interest, our results
support the use of free-electron-induced light emission from spherically
symmetric systems as a versatile platform for the generation of chiral light
with on-demand control over the phase and degree of polarization
Genetic diversity and character association analysis based on pomological traits in olive (Olea europaea L.)
Thirteen exotic genotypes of olive (Olea europaea L.) were studied for the genetic variability, correlation and path coefficient analysis for fruit quality, yield and yield contributing traits at experimental farm of ICAR-CITH, Srinagar during 2009-2013. Maximum variability was recorded for fruit yield and oil content, however, low differ-ences between the phenotypic and genotypic coefficients of variations indicated low environmental influences on the expression of these characters. High heritability coupled with high genetic advance was obtained with fruit yield per plant, acidity, fruit pulp weight, fruit weight and stone weight. Fruit weight (r=0.329), stone weight (r=0.405) and oil content (r=0.841) were the most important traits, which possessed significant positive association with fruit yield per plant. Path coefficient analysis revealed that among the different yield contributing characters oil content (0.875), fruit weight (0.797) followed by acidity (0.501), peroxides value ( 0.199) and fruit length (0.054) influenced fruit yield per plant directly. The direct effects of these characters on fruit yield were found positive and considerably very high.The selection based on fruit weight, stone weight oil content and yield per plant will be effective for enhancing the fruit and oil yieldand making future olive breeding strategies
From attosecond to zeptosecond coherent control of free-electron wave functions using semi-infinite light fields
Light-electron interaction in empty space is the seminal ingredient for
free-electron lasers and also for controlling electron beams to dynamically
investigate materials and molecules. Pushing the coherent control of free
electrons by light to unexplored timescales, below the attosecond, would enable
unprecedented applications in light-assisted electron quantum circuits and
diagnostics at extremely small timescales, such as those governing
intramolecular electronic motion and nuclear phenomena. We experimentally
demonstrate attosecond coherent manipulation of the electron wave function in a
transmission electron microscope, and show that it can be pushed down to the
zeptosecond regime with existing technology. We make a relativistic pulsed
electron beam interact in free space with an appropriately synthesized
semi-infinite light field generated by two femtosecond laser pulses reflected
at the surface of a mirror and delayed by fractions of the optical cycle. The
amplitude and phase of the resulting coherent oscillations of the electron
states in energymomentum space are mapped via momentum-resolved ultrafast
electron energy-loss spectroscopy. The experimental results are in full
agreement with our theoretical framework for light-electron interaction, which
predicts access to the zeptosecond timescale by combining semi-infinite X-ray
fields with free electrons.Comment: 22 pages, 6 figure
Petahertz optical response in graphene
The temporal dynamics of charge carriers determines the speed with which
electronics can be realized in condensed matter, and their direct manipulation
with optical fields promises electronic processing at unprecedented petahertz
frequencies, consisting in a million-fold increase from state of the art
technology. Graphene is of particular interest for the implementation of
petahertz optoelectronics due to its unique transport properties, such as high
carrier mobility with near-ballistic transport and exceptionally strong
coupling to optical fields. The back action of carriers in response to an
optical field is therefore of key importance towards applications. Here we
investigate the instantaneous response of graphene to petahertz optical fields
and elucidate the role of hot carriers on a sub-100 fs timescale. Measurements
of the nonlinear response and its dependence on interaction time and field
polarization allow us to identify the back action of hot carriers over
timescales that are commensurate with the optical field. An intuitive picture
is given for the carrier trajectories in response to the optical-field
polarization state. We note that the peculiar interplay between optical fields
and charge carriers in graphene may also apply to surface states in topological
insulators with similar Dirac cone dispersion relations.Comment: 6 pages, 4 figure