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The properties of unusual surface plasmon modes and switching gaps in the three-dimensional photonic crystals composed of plasma-coated spheres

In this paper, the surface plasmon modes and switching gaps of three-dimensional (3D) photonic crystals (PCs) with diamond lattices, which are composed of core isotropic dielectric spheres surrounded by plasma shells inserted in air, are theoretically investigated in detail based on a modified plane wave expansion method. The equations for computing band structures for such 3D PCs are presented. Our analyses show that the proposed double-shell structure can produce the complete photonic band gaps (PBGs) which can be worked as an optical switching by manipulating the parameters of such PCs. However, the switching state cannot be tuned by the plasma collision frequency. Numerical results also demonstrate that a flatbands region and the stop band gaps (SBGs) in the (1 0 0) and (1 1 1) directions which are above the flatbands region can be achieved. The SBGs also can be tuned by the parameters as mentioned above. There is also a threshold value for the thickness of plasma shell, which can make the band structures of the 3D PCs with double-shell structures similar to those obtained from the same PC structure containing the pure plasma spheres. In this case, the dielectric function of the inserted core sphere will not affect the band structures. It means that the PBGs can be achieved by replacing the pure plasma spheres with such double-shell structures to make fabrication possible and save the material in the realization. It is also noticed that the flatbands region is determined by the existence of surface plasmon modes, and the upper edge of flatbands region does not depend on the topology of lattice.