In the beetle Goliathus cacicus, male elytra show silky luster with iridescence while female ones appear lusterless white without iridescence to our perception. We revealed by structural characterizations and optical measurements that elytral coloration and luster of both male and female beetles stem from the tubular scales on the elytra, whose interior is filled with a random structure. Distinct differences between male and female scales reside in the cortex thickness and the filling fraction of the random structure, which are important factors in the determination of the sexual dichromatic luster and iridescence. In additional to reflection peaks in the visible range, spectral measurements indicate that both male and female elytra display also strong iridescent ultraviolet (UV) reflections. Scattering spectra show that both male and female elytra display UV luster, although it is absent for female ones in the visible range.
Composite nanoparticles （NPs） have the ability of combining materials with different properties together, thus receiving extensive attention in many fields. Here we theoretically investigate the electric field distribution around core/shell NPs （a type of composite NPs） in ferrofluids under the influence of an external magnetic field. The NPs are made of cobalt （ferromagnetic） coated with gold （metallic）. Under the influence of the external magnetic field, these NPs will align along the direction of this field, thus forming a chain of NPs. According to Laplace＇s equations, we obtain electric fields inside and outside the NPs as a function of the incident wavelength by taking into account the mutual interaction between the polarized NPs. Our calculation results show that the electric field distribution is closely related to the resonant incident wavelength, the metallic shell thickness, and the inter-particle distance. These analytical calculations agree well with our numerical simulation results. This kind of field-induced anisotropic soft-matter systems offers the possibility of obtaining an enhanced Raman scattering substrate due to enhanced electric fields.
We discuss a new class of phenomena that we call ＂spin plasmonics＂. It is motivated by three different recent trends of physics research： （i） spintronics, （ii） plasmonics, and （iii） topological properties as is exemplified by the quantized Hall effect. This involves the physics of the ＂magnetic surface plasmon＂ （MSP） which provides for an analog of the edge states discussed in the quantized Hall effect. Their properties can be easily tuned by an external magnetic field. They are coupled to the electromagnetic field and can be injected into metallic structures and induce spin and charge currents and hold the promise of miniturization of nonreciprocal devices.
Based on a first-principles approach,we establish an alternating-current（AC） relaxation theory for a rotating metallic particle with complex dielectric constant εα=εα-iσα/ω0.Here εα is the real part,σα the conductivity,ω0 the angular frequency of an AC electric field,and i=-11/2.Our theory yields an accurate interparticle force,which is in good agreement with the existing experiment.The agreement helps to show that the relaxations of two kinds of charges,namely,surface polarized charges（described by εα） and free charges（corresponding to σα）,contribute to the unusually large reduction in the attracting interparticle force.This theory can be adopted to determine the relaxation time of dynamic particles in various fields.
We theoretically investigate the photonic band gap in one-dimensional photonic crystals with a graded multilayer structure. The proposed structure constitutes an alternating composite layer （metallic nanoparticles embedded in TiO2 film） and an air layer. Regarding the multilayer as a series of capacitance, effective optical properties are derived. The dispersion relation is obtained with the solution of the transfer matrix equation. With a graded structure in the composite layer, numerical results show that the position and width of the photonic band gap can be effectively modulated by varying the number of the graded composite layers, the volume fraction of nanoparticles and the external stimuli.
