This can lead to a strong change in
the resonant transmission and reflection of the hybrid. Prime candidates
for hybridization with metamaterials
are semiconductors and semiconductor multiple-quantum-well structures
used as substrates for a metallic framework, carbon nanotubes and fullerenes
implanted into the fabric of the metamaterials and organic nonlinear media.
Scientists have already demonstrated
the ability to change a metamaterial’s
response at terahertz frequencies by
injection or optical generation of free-carriers into a gallium-arsenide substrate. Recent experiments show that the
ultrafast nonlinear response of silicon
can be strongly enhanced by adding a
metamaterial layer. Single-wall semiconductor carbon nanotubes deposited
on metamaterials exhibit an order-of-magnitude higher nonlinearity than the
already extremely strong response of the
nanotubes themselves, due to a resonant
plasmon-exciton interaction.
So-called “phase-change” materials are prime agents for switching:
chalcogenide glasses have been used
in rewritable optical disk technology
for several decades. They provide fast
and reproducible changes in optical
properties in response to excitation. This
functionality is underpinned by phase
transitions between crystalline and
amorphous states and may be engaged
by optical or electrical stimulation: A
nanoscale metamaterial electro-optical
Graphene is another
favorite that promises
to add electro-optical
capability to meta-
materials, in particular
in the IR and terahertz
domains, by exploiting
the spectral shift
of electromagnetic
response driven by
applied voltage.
domains, by exploiting the spectral shift
of electromagnetic response driven by
applied voltage. A recent demonstration
of the magnetic control of plasmons in
layered structures of ferroelectric and
noble metals can also be translated to
the tuning of metamaterials.
switch using chalcogenide glass has
been demonstrated.
Similar properties are exhibited by
transition metal oxides, in particular
vanadium dioxide. In another example,
the transition between different metastable phases in polymorphic elemental
gallium leads to dramatic change in
dielectric and plasmonic properties,
making it another candidate for use in
switchable metamaterials, alongside
with liquid crystals.
A very substantial change in the
dielectric properties of a nanometer-thick layer may be achieved in conductive oxides through the injection of
free-carriers, which should be enough
to control resonant transmission in
a hybrid metamaterial. Graphene is
another favorite that promises to add
electro-optical capability to metamaterials, in particular in the IR and terahertz
Sensor applications
Sensor applications represent another
rapidly growing area in metamaterials
research. For instance, asymmetrically
split ring resonators supporting high-quality Fano resonances or metamaterial
arrays of nanoscale antennas are well
suited to detecting low-concentration
analytes such as sugar, hydrogen, etc.,
through variations in their transmission and reflection characteristics. A
single molecular layer of graphene, for
example, can induce a multifold change
in the transmission of a metamaterial.
Plasmonic metamaterial nanostructures
can also be used to improve light-har-vesting solutions, permitting a considerable reduction in physical thickness and
improved efficiency in solar photovoltaic
absorber layers.
[ Conventional metamaterials vs. future “quantum metamaterials” ]
Conventional metamaterials Superconducting metamaterials
(current paradigm) (future paradigm)
Split ring—classical Josephson quantum-mechanical
plasmonic resonator interference device
Building block of
the technology
Excitation/
information carrier
Mode of operation
Frequency range
Plasmon
Supercurrent/quantum qubit
Analog
From microwave to optical
Advantages
Simplicity
Quantized (“digital”)
Main challenges
Losses and challenging
fabrication for applications in
the visible part of the spectrum
Sophisticated fabrication and
need for cryo-cooling
Superconducting and
quantum metamaterials
Superconducting metamaterials have
recently emerged to offer a radically
new paradigm for data processing and
information technologies. They will
provide a dramatic reduction of losses,
accompanied by access to the extreme
sensitivity of the superconducting state
to external stimuli and the exceptional
nonlinearity of superconductors (orders
of magnitude higher than p-n junctions),
enabling low energy switching at the
subattojoule level.
Negative dielectric constants and
dominant kinetic resistance also make
superconductors an intriguing plasmonic
media. Moreover, a fundamental change
in the nature of information carriers is
produced by superconductivity: In some
implementations, it will be possible to
switch from the classical excitations of
conventional plasmonic and metamaterial devices to quantum excitations
