16,568 research outputs found
Wavevector Selective Metasurfaces and Tunnel Vision Filters
Metasurfaces offer unprecedented flexibility in the design and control of
light propagation, replacing bulk optical components and exhibiting exotic
optical effects. One of the basic properties of the metasurfaces, which renders
them as frequency selective surfaces, is the ability to transmit or reflect
radiation within a narrow spectral band that can be engineered on demand. Here
we introduce and demonstrate experimentally in the THz domain the concept of
wavevector selective surfaces -- metasurfaces transparent only within a narrow
range of light propagation directions operating effectively as tunnel vision
filters. Practical implementations of the new concept include applications in
wavefront manipulation, observational instruments, vision and free-space
communication in light-scattering environments, as well as passive camouflage
Micromagnetic understanding of stochastic resonance driven by spin-transfertorque
In this paper, we employ micromagnetic simulations to study non-adiabatic
stochastic resonance (NASR) excited by spin-transfer torque in a
super-paramagnetic free layer nanomagnet of a nanoscale spin valve. We find
that NASR dynamics involves thermally activated transitions among two static
states and a single dynamic state of the nanomagnet and can be well understood
in the framework of Markov chain rate theory. Our simulations show that a
direct voltage generated by the spin valve at the NASR frequency is at least
one order of magnitude greater than the dc voltage generated off the NASR
frequency. Our computations also reproduce the main experimentally observed
features of NASR such as the resonance frequency, the temperature dependence
and the current bias dependence of the resonance amplitude. We propose a simple
design of a microwave signal detector based on NASR driven by spin transfer
torque.Comment: 25 pages 8 figures, accepted for pubblication on Phys. Rev.
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