Liu Yingkai

Electrically tunable resonant terahertz transmission in subwavelength hole arrays

An actively enhanced resonant transmission in a plasmonic array of subwavelength holes is demonstrated by use of terahertz time-domain spectroscopy. By connecting this two-dimensional element into an electrical circuit, tunable resonance enhancement is observed in arrays made from good and relatively poor metals. The tunable feature is attributed to the nonlinear electric response of the periodic hole array film, which is confirmed by its voltage—current behavior. This finding could lead to a unique route to active plasmonic devices, such as tunable filters, spatial modulators, and integrated terahertz optoelectronic components.

Influence of defect states on band gaps in the two-dimensional phononic crystal of 4340 steel in an epoxy

The band structures of a new two-dimensional triangle-shaped array geometry of 4340 steel cylinders of square cross section in an epoxy resin were studied by the plane-wave expansion and supercell calculation method. The band gaps of this type of phononic crystals with different defects were calculated such as defect-free, 60° crystal linear defect states, 120° crystal linear defect states, and 180° crystal linear defect states. It was found that the band gap will emerge in different linear defects of the phononic crystals and the bandwidth of linear defect states is larger than that of the free-defect crystal by about 2.14 times within the filling fraction F = 0.1–0.85. In addition, the influence of the filling fraction on the relative width of the minimum band gap is discussed.

Electronic structure and magnetic properties of (Mn, N)-codoped ZnO

The electronic structures and magnetic properties of (Mn, N)-codoped ZnO are investigated by using the first-principles calculations. In the ferromagnetic state, as N substitutes for the intermediate O atom of the nearest neighboring Mn ions, about 0.5 electron per Mn2+ ion transfers to the N2− ion, which leads to the high-state Mn ions (close to +2.5) and trivalent N3− ions. In an antiferromagnetic state, one electron transfers to the N2− ion from the downspin Mn2+ ion, while no electron transfer occurs for the upspin Mn2+ ion. The (Mn, N)-codoped ZnO system shows ferromagnetism, which is attributed to the hybridization between Mn 3d and N 2p orbitals.