Surface magnetoplasmon (SMP) supported at an interface between magnetized plasmonic and dielectric materials has been widely explored; however, it suffers with narrow bandwidth for one-way propagation. Here we propose a novel metal-semiconductor-dielectricmetal (MSDM) structure showing the large bandwidth for the complete one-way propagation (COWP). Because of the compression of the zone for two-way propagating modes in the semiconductor layer by reducing semiconductor thickness, the bandwidth is significantly increased by several times. More importantly, in such MSDM structure, the SMP dispersion can be engineered by controlling the semiconductor thickness, and based on this, slowing wave and trapping rainbow can be realized in a tapered system at terahertz frequencies.
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Trapped rainbow effects have been realized in many systems while they are all characterized by electric-field enhancement. The trapped rainbow with strong magnetic-field enhancement has yet to be studied. Here, we achieve the trapped magnetic rainbow effect in a novel metal-air-YIG (yttrium-iron-garnet)-metal (MAYM) waveguide applied with a continuously decreasing magnetic field. The proposed system supports a one-way propagation feature, leading to the suppressed reflection. We systemically analyze the dispersion and the modal properties, showing the transition from the SMP (surface magnetoplasmon)-like mode to magnetostatic-like mode and the change of the group velocity when decreasing the external magnetic field along the propagation direction of the wave. We obtain the trapped magnetic rainbow effects as well as magnetic hotspots both in frequency-and time-domain simulations. The trapped rainbow effect with strong magnetic field enhancement paves a promising way for many applications including magnetic sensing to magnetic non-linearity.
The subwavelength focusing based on surface plasmon polaritons (SPP) has been widely explored in tapered metallic structures. However, the efficiency of energy localization is relatively weak, largely due to high propagation loss and strong back reflection. Here, we propose a straight-tapered 3-dimensional (3D) one-way surface magnetoplasmon (SMP) waveguide with the ending surface of ∼ 10 −4 λ 0 × 10 −4 λ 0 to achieve energy focusing in the microwave regime. Due to low propagation loss of SMP, we achieve huge magnetic field enhancement in such an ultra-subwavelength area, by five orders of magnitude. Instead of using an external static magnetic field, our proposed SMP waveguide relies on remanence, which is very convenient for operating practical 3D applications. These results show promising applications in magnetic-field enhancing or quenching fluorescence, luminescence or nonlinearity of 2D materials, novel scanning near-field microwave microscopy and energy storage.
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