Based on a structure consisting of a single graphene layer situated on a periodic dielectric grating, we show theoretically that intense terahertz (THz) radiations can be generated by an electron bunch moving atop the graphene layer. The underlying p
hysics lies in the fact that a moving electron bunch with rather low electron energy ($sim$1 keV) can efficiently excite graphene plasmons (GPs) of THz frequencies with a strong confinement of near-fields. GPs can be further scattered into free space by the grating for those satisfying the phase matching condition. The radiation patterns can be controlled by varying the velocity of the moving electrons. Importantly, the radiation frequencies can be tuned by varying the Fermi level of the graphene layer, offering tunable THz radiations that can cover a wide frequency range. Our results could pave the way toward developing tunable and miniature THz radiation sources based on graphene.
We study the nonlocal spin and charge current generation in a finite metallic element on the surface of magnetic insulators such as tcb{yttrium iron garnet} due to the absorption of the magnetic surface plasmon (MSP). Whereas a surface plasmon is com
pletely reflected by a metal, tcb{an} MSP tcb{can be} absorbed tcb{due to the absence of backward states}. The tcb{injection of} MSP generates a voltage in the longitudinal direction parallel to the wave vector, tcb{with the voltage} proportional to input power. If the metal is a ferromagnet, a spin current can also be tcb{induced} in the longitudinal direction. Our tcb{results provide a way to improve upon} integrated circuits of spintronics and spin wave logic devices.
When an oscillating line source is placed in front of a special mirror consisting of an array of flat uniformly spaced ferrite rods, half of the image disappeared at some frequency. We believe that this comes from the coupling to photonic states of t
he magnetic surface plasmon band. These states exhibit giant circulations that only go in one direction due to time reversal symmetry breaking. Possible applications of this rectifying reflection include a robust one-way waveguide, a 90 degree beam bender and a beam splitter, which are shown to work even in the deep subwavelength scale.
We solve {bf analytically} the multiple scattering (KKR) equations for the two dimensional photonic crystals in the long wavelength limit. Different approximations of the electric and magnetic susceptibilities are presented from a unified pseudopoten
tial point of view. The nature of the so called plasmon-polariton bands are clarified. Its frequency as a function of the wire radius is discussed.
We derived simple polynomial equations to determine the entire resonance spectra of split ring structures. For double stacking split rings made with flat wires, we showed that the resonance frequency depends linearly on the ring-ring separation. In p
articular, we found that the wavelength of the lowest resonance mode can be made as large as the geometrical size of the ring for realistic experimental conditions, whereas for current systems this ratio is of the order of 10. Finite-difference-time-domain simulations on realistic structures verified the analytic predictions.
We studied the response of a ferromagnet-insulator-normal metal tunnel structure under an external oscillating radio frequency (R.F.) magnetic field. The D. C. voltage across the junction is calculated and is found not to decrease despite the high re
sistance of the junction; instead, it is of the order of $mu V$ to $100mu V$, much larger than the experimentally observed value (100 nano-V) in the strong coupled ohmic ferromagnet-normal metal bilayers. This is consistent with recent experimental results in tunnel structures, where the voltage is larger than $mu V$s. The damping and loss of an external RF field in this structure is calculated.
