Induced circular dichroism (ICD) is found between plasmonic nanostructures and chiral molecules, where at least one of them is chiral. However, it is a great challenge to generate ICD only through achiral structures with the simple coupling model. Here, we demonstrate that ICD is approximately contributed by the cross-electromagnetic coupling between equivalent electric dipole moments and magnetic dipole moments for two achiral plasmon nanostructures. To prove electromagnetic couplings between different wavebands, graphene belts are introduced into plasmon nanostructures composing achiral metal-nanorods with graphene-nanobelt arrays (AMGAs). Results showed that ICD signals are achieved in a near-infrared band of metal resonance and a micron band of graphene resonance. Near-field charge distributions of AMGAs reveal the coupling effect between metal-nanorods and graphene-nanobelts. The handedness of AMGAs can be actively controlled by adjusting the Fermi levels of graphenenanobelts; the strength and resonant wavelength of ICD can be tuned by adjusting the geometric parameters of AMGAs. Besides, AMGAs can enhance the CD signal of chiral molecules with different handedness. The maximum enhancement factor of chiral molecules could reach up to 800 times in a near-infrared band and 600 times in a micron band. These results are helpful to design dynamically tunable chiral sensors in biological monitoring and analytical chemistry.
A method, believed to be new, to simulate Drude parameters for collective oscillation of the free carriers in metallic films is proposed. Plasma resonance frequency and relaxation were simulated simultaneously from both the real and the imaginary parts of the dielectric function of a metallic film after consideration of their correlation in the Drude model. As examples, the contributions of the electrons in Ag films and of the free carriers in metallic silicide, NbSi(2) and TaSi(2), films have been studied.
The magneto-optical and optical properties of GdFe single layer films, which are covered with a thin Si3N4 layer, were studied in the visible wavelength region. A Kerr rotation peak and a reflectivity drop were observed near 4.1 eV in GdFe alloyed films and attributed to the Gd element. Compared with the single thick GdFe film, the Kerr effect of SiN/GdFe bilayers was enhanced, due to the optical interference between Si3N4 and GdFe. The Kerr rotation of GdFe films showed a nonlinear function of the compositions in the whole measured wavelength range. Magneto-optical measurements directly evidence the spin–flip in the GdFe films as the Gd content increased from 20.7 to 24.2 at. %, which showed advantages over conventional magnetometry.
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