48,715 research outputs found
Tunability of Superconducting Metamaterials
Metamaterials are artificial structures with unique electromagnetic
properties, such as relative dielectric permittivity and magnetic permeability
with values less than 1, or even negative. Because these properties are so
sensitive to loss, we have developed metamaterials comprised of superconducting
waveguides, wires, and split-ring resonators. An important requirement for
applications of these metamaterials is the ability to tune the frequency at
which the unique electromagnetic response occurs. In this paper we present
three methods (unique to superconductors) to accomplish this tuning:
temperature, dc magnetic field, and rf magnetic field. Data are shown for dc
and rf magnetic field tuning of a single Nb split-ring resonator (SRR). It was
found that the dc field tuning was hysteritic in the resonant frequency data,
while the quality factor, , was less hystertic. The rf power tuning showed
no hysteresis, but did show supression of the at high power.
Magneto-optical images reveal inhomogeneous magnetic vortex entry in the dc
field tuning, and laser scanning photoresponse images for a
YBaCuO SRR reveals the current distribution in the rings.Comment: RexTEX, 4 pages of text with 6 figures plus 1/5 page of references,
submitted for the 2006 Applied Superconductivity Conference; Revised edition:
spelling corrections, and we removed mention of measuring the Current Density
and replaced this with a more explicit definition of what we measure (with
reference
Structural tunability in metamaterials
We propose a novel approach for efficient tuning of the transmission
characteristics of metamaterials through a continuous adjustment of the lattice
structure, and confirm it experimentally in the microwave range. The concept is
rather general and applicable to various metamaterials as long as the effective
medium description is valid. The demonstrated continuous tuning of metamaterial
response is highly desirable for a number of emerging applications of
metamaterials including sensors, filters, switches, realizable in a wide
frequency range
Plasmon tunability in metallodielectric metamaterials
The dielectric properties of metamaterials consisting of periodically
arranged metallic nanoparticles of spherical shape are calculated by rigorously
solving Maxwell's equations. Effective dielectric functions are obtained by
comparing the reflectivity of planar surfaces limiting these materials with
Fresnel's formulas for equivalent homogeneous media, showing mixing and
splitting of individual-particle modes due to inter-particle interaction.
Detailed results for simple cubic and fcc crystals of aluminum spheres in
vacuum, silver spheres in vacuum, and silver spheres in a silicon matrix are
presented. The filling fraction of the metal f is shown to determine the
position of the plasmon modes of these metamaterials. Significant deviations
are observed with respect to Maxwell-Garnett effective medium theory for large
f, and multiple plasmons are predicted to exist in contrast to Maxwell-Garnett
theory.Comment: 6 pages, 4 figure
Interferometric tunability of the absorption
We propose an interferometric setup that permits to tune the quantity of
radiation absorbed by an object illuminated by a fixed light source. The method
can be used to selectively irradiate portions of an object based on their
transmissivities or to accurately estimate the transmissivities from rough
absorption measurements.Comment: 4 pages, 5 figures. Revised in response to the comments of the
referees. Section added with new materia
On-Demand Spin-Orbit Interaction from Which-Layer Tunability in Bilayer Graphene
Spin-orbit interaction (SOI) that is gate-tunable over a broad range is
essential to exploiting novel spin phenomena. Achieving this regime has
remained elusive because of the weakness of the underlying relativistic
coupling and lack of its tunability in solids. Here we outline a general
strategy that enables exceptionally high tunability of SOI through creating a
which-layer spin-orbit field inhomogeneity in graphene multilayers. An external
transverse electric field is applied to shift carriers between the layers with
strong and weak SOI. Because graphene layers are separated by sub-nm scales,
exceptionally high tunability of SOI can be achieved through a minute carrier
displacement. A detailed analysis of the experimentally relevant case of
bilayer graphene on a semiconducting transition metal dichalchogenide substrate
is presented. In this system, a complete tunability of SOI amounting to its
ON/OFF switching can be achieved. New opportunities for spin control are
exemplified with electrically driven spin resonance and topological phases with
different quantized intrinsic valley Hall conductivities.Comment: 8 pages, 3 figure
Wide frequency tuning of continuous terahertz wave generated by difference frequency mixing under exciton-excitation conditions in a GaAs/AlAs multiple quantum well
Continuous terahertz wave sources with narrow bandwidth and wide frequency tunability enable high-resolution terahertz spectroscopy and high-speed information communication. In this study, using the optical nonlinearity of excitons as the source of second-order nonlinear polarization, we realize a continuous terahertz electromagnetic wave demonstrating wide frequency tunability from 0.1 to 18 THz without a decrease in intensity due to phonon scattering. Because of excitation of two exciton states in a
Ga
As
/
Al
As
multiple quantum well using two continuous-wave lasers, terahertz waves are emitted as a result of difference-frequency mixing, where the intensity shows a square dependence on the excitation intensity. Using the inhomogeneous width of exciton lines, we achieve wide frequency tunability without phonon effects
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