991 research outputs found
Quantized beam shifts in graphene
We predict quantized Imbert-Fedorov, Goos-H\"anchen, and photonic spin Hall
shifts for light beams impinging on a graphene-on-substrate system in an
external magnetic field. In the quantum Hall regime the Imbert-Fedorov and
photonic spin Hall shifts are quantized in integer multiples of the fine
structure constant , while the Goos- H\"anchen ones in multiples of
. We investigate the influence on these shifts of magnetic field,
temperature, and material dispersion and dissipation. An experimental
demonstration of quantized beam shifts could be achieved at terahertz
frequencies for moderate values of the magnetic field.Comment: Correction of typos, title change, and updated references. 5 pages, 4
figure
Topological Phase Transitions and Quantum Hall Effect in the Graphene Family
Monolayer staggered materials of the graphene family present intrinsic
spin-orbit coupling and can be driven through several topological phase
transitions using external circularly polarized lasers, and static electric or
magnetic fields. We show how topological features arising from photo-induced
phase transitions and the quantum Hall effect coexist in these materials, and
simultaneously impact their Hall conductivity through their corresponding
charge Chern numbers. We also show that the spectral response of the
longitudinal conductivity contains signatures about the various phase
transition boundaries, that the transverse conductivity encodes information
about the topology of the band structure, and that both present resonant peaks
which can be unequivocally associated to one of the four inequivalent Dirac
cones present in these materials. This complex optoelectronic response can be
probed with straightforward Faraday rotation experiments, allowing the study of
the crossroads between quantum Hall physics, spintronics, and valleytronics.Comment: 8 pages, 6 figure
Molding the flow of light with a magnetic field: plasmonic cloaking and directional scattering
We investigate electromagnetic scattering and plasmonic cloaking in a system
composed by a dielectric cylinder coated with a magneto-optical shell. In the
long-wavelength limit we demonstrate that the application of an external
magnetic field can not only switch on and off the cloaking mechanism but also
mitigate losses, as the absorption cross-section is shown to be minimal
precisely at the cloaking operation frequency band. We also show that the
angular distribution of the scattered radiation can be effectively controlled
by applying an external magnetic field, allowing for a swift change in the
scattering pattern. By demonstrating that these results are feasible with
realistic, existing magneto-optical materials, such as graphene epitaxially
grown on SiC, we suggest that magnetic fields could be used as an effective,
versatile external agent to tune plasmonic cloaks and to dynamically control
electromagnetic scattering in an unprecedented way, we hope that these results
may find use in disruptive photonic technologies.Comment: 7 pages, 8 figure
Tuning plasmonic cloaks with an external magnetic field
We propose a mechanism to actively tune the operation of plasmonic cloaks
with an external magnetic field by investigating electromagnetic scattering by
a dielectric cylinder coated with a magneto-optical shell. In the long
wavelength limit we show that the presence of an external magnetic field may
drastically reduce the scattering cross-section at all observation angles. We
demonstrate that the application of external magnetic fields can modify the
operation wavelength without the need of changing material and/or geometrical
parameters. We also show that applied magnetic fields can reversibly switch on
and off the cloak operation. These results, which could be achieved for
existing magneto-optical materials, are shown to be robust to material losses,
so that they may pave the way for developing actively tunable, versatile
plasmonic cloaks.Comment: 5 pages and 4 figures Figure 4 has been remad
Enhancing Near-Field Heat Transfer in Composite Media: Effects of the Percolation Transition
We investigate the near-field heat transfer between a semi-infinite medium
and a nanoparticle made of composite materials. We show that, in the effective
medium approximation, the heat transfer can be greatly enhanced by considering
composite media, being maximal at the percolation transition. Specifically, for
titanium inclusions embedded in a polystyrene sphere, this enhancement can be
up to thirty times larger than in the case of the corresponding homogeneous
titanium sphere. We demonstrate that our findings are robust against material
losses, to changes in the shape of inclusions and materials, and apply for
different effective medium theories. These results suggest the use of composite
media as a new, versatile material platform to enhance, optimize, and tailor
near-field heat transfer in nanostructures.Comment: 8 pages, 6 figures, 2 table
Purcell effect at metal-insulator transitions
We investigate the spontaneous emission rate of a two-level quantum emitter
next to a composite medium made of randomly distributed metallic inclusions
embedded in a dielectric host matrix. In the near-field, the Purcell factor can
be enhanced by two-orders of magnitude relative to the case of an homogeneous
metallic medium, and reaches its maximum precisely at the insulator-metal
transition. By unveiling the role of the decay pathways on the emitter's
lifetime, we demonstrate that, close to the percolation threshold, the
radiation emission process is dictated by electromagnetic absorption in the
heterogeneous medium. We show that our findings are robust against change in
material properties, shape of inclusions, and apply for different effective
medium theories as well as for a wide range of transition frequencies.Comment: 8 pages, 7 figure
Tuning quantum fluctuations with an external magnetic field: Casimir-Polder interaction between an atom and a graphene sheet
We investigate the dispersive Casimir-Polder interaction between a Rubidium
atom and a suspended graphene sheet subjected to an external magnetic field B.
We demonstrate that this concrete physical system allows for an unprecedented
control of dispersive interactions at micro and nanoscales. Indeed, we show
that the application of an external magnetic field can induce a 80% reduction
of the Casimir-Polder energy relative to its value without the field. We also
show that sharp discontinuities emerge in the Casimir-Polder interaction energy
for certain values of the applied magnetic field at low temperatures. Moreover,
for sufficiently large distances these discontinuities show up as a
plateau-like pattern with a quantized Casimir-Polder interaction energy, in a
phenomenon that can be explained in terms of the quantum Hall effect. In
addition, we point out the importance of thermal effects in the Casimir-Polder
interaction, which we show that must be taken into account even for
considerably short distances. In this case, the discontinuities in the
atom-graphene dispersive interaction do not occur, which by no means prevents
the tuning of the interaction in ~50% by the application of the external
magnetic field.Comment: The first two authors listed contributed equally to this work and are
joint first authors. 5 pages, 4 figure
Microscale electromagnetic heating in heterogeneous energetic materials based on X-ray CT imaging
Electromagnetic stimulation of energetic materials provides a noninvasive and
nondestructive tool for detecting and identifying explosives. We combine
structural information based on X-ray computed tomography, experimental
dielectric data, and electromagnetic full-wave simulations, to study microscale
electromagnetic heating of realistic three-dimensional heterogeneous
explosives. We analyze the formation of electromagnetic hot spots and thermal
gradients in the explosive-binder meso-structures, and compare the heating rate
for various binder systems.Comment: 8 pages, 5 figure
Metasurface Broadband Solar Absorber
We demonstrate a broadband, polarization independent, omnidirectional
absorber based on a metallic metasurface architecture, which accomplishes
greater than 90% absorptance in the visible and near-infrared range of the
solar spectrum, and exhibits low emissivity at mid- and far-infrared
wavelengths. The complex unit cell of the metasurface solar absorber consists
of eight pairs of gold nano-resonators that are separated from a gold ground
plane by a thin silicon dioxide spacer. Our experimental measurements reveal
high-performance absorption over a wide range of incidence angles for both s-
and p-polarizations. We also investigate numerically the frequency-dependent
field and current distributions to elucidate how the absorption occurs within
the metasurface structure. Furthermore, we discuss the potential use of our
metasurface absorber design in solar thermophotovoltaics by exploiting
refractory plasmonic materials
Two-photon spontaneous emission in atomically thin plasmonic nanostructures
The ability to harness light-matter interactions at the few-photon level
plays a pivotal role in quantum technologies. Single photons - the most
elementary states of light - can be generated on-demand in atomic and solid
state emitters. Two-photon states are also key quantum assets, but achieving
them in individual emitters is challenging because their generation rate is
much slower than competing one-photon processes. We demonstrate that atomically
thin plasmonic nanostructures can harness two-photon spontaneous emission,
resulting in giant far-field two-photon production, a wealth of resonant modes
enabling tailored photonic and plasmonic entangled states, and plasmon-assisted
single-photon creation orders of magnitude more efficient than standard
one-photon emission. We unravel the two-photon spontaneous emission channels
and show that their spectral line-shapes emerge from an intricate interplay
between Fano and Lorentzian resonances. Enhanced two-photon spontaneous
emission in two-dimensional nanostructures paves the way to an alternative
efficient source of light-matter entanglement for on-chip quantum information
processing and free-space quantum communications.Comment: 13 pages, 4 figure
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