Dramatically Enhanced Spin Dynamo with Plasmonic Diabolo Cavity.

The applications of spin dynamos, which could potentially power complex nanoscopic devices, have so far been limited owing to their extremely low energy conversion efficiencies. Here, we present a unique plasmonic diabolo cavity (PDC) that dramatically improves the spin rectification signal (enhancement of more than three orders of magnitude) under microwave excitation; further, it enables an energy conversion efficiency of up to ~0.69 mV/mW, compared with ~0.27 µV/mW without a PDC. This remarkable improvement arises from the simultaneous enhancement of the microwave electric field (~13-fold) and the magnetic field (~195-fold), which cooperate in the spin precession process generates photovoltage (PV) efficiently under ferromagnetic resonance (FMR) conditions. The interplay of the microwave electromagnetic resonance and the ferromagnetic resonance originates from a hybridized mode based on the plasmonic resonance of the diabolo structure and Fabry-Perot-like modes in the PDC. Our work sheds light on how more efficient spin dynamo devices for practical applications could be realized and paves the way for future studies utilizing both artificial and natural magnetism for applications in many disciplines, such as for the design of future efficient wireless energy conversion devices, high frequent resonant spintronic devices, and magnonic metamaterials.

Metamaterial perfect absorbers with solid and inverse periodic cross structures for optoelectronic applications.

Metamaterial based on a metal/insulator/metal (MIM) tri-layer structure provides an agile platform to realize high absorption efficiency for a variety of applications including semiconductor optoelectronic detectors. In this work, we use the finite time domain difference (FDTD) method and coupled mode theory (CMT) to numerically study metal/semiconductor/metal (MSM) structures and discuss their effective absorption for optoelectronic application. We compare MSM structures with a different top metal layer design and find that cross shaped absorber (CSA) and it's complementary cross shaped absorber (CCSA) exhibit different phase diagrams due to a distinctive dependence of radiation loss on geometrical parameters. Our results show that CSA (CCSA) structures are suitable for thinner (thicker) sandwiched semiconductor with a larger (smaller) imaginary part of its dielectric constant. The necessary condition to realize a maximum figure of merit (FOM) value for effective absorption is discussed in comparison with the perfect absorber condition. Our work may provide guidelines to design the general light-harvesting optoelectronic devices with high efficiencies based on metamaterial-semiconductor hybrid systems.

Multiband Hot Photoluminescence from Nanocavity-Embedded Silicon Nanowire Arrays with Tunable Wavelength.

Besides the well-known quantum confinement effect, hot luminescence from indirect bandgap Si provides a new and promising approach to realize monolithically integrated silicon optoelectronics due to phonon-assisted light emission. In this work, multiband hot photoluminescence is generated from Si nanowire arrays by introducing trapezoid-shaped nanocavities that support hybrid photonic-plasmonic modes. By continuously adjusting the geometric parameters of the Si nanowires with trapezoidal nanocavities, the multiband hot photoluminescence can be tuned in the range from visible to near-infrared independent of the excitation laser wavelength. The highly tunable wavelength bands and concomitant compatibility with Si-integrated electronics enable tailoring of silicon-based light sources suitable for next-generation optoelectronics devices.

Design of triple-band metamaterial absorbers with refractive index sensitivity at infrared frequencies.

A triple-band perfect plasmonic metamaterial absorber based on a metal/insulator/metal (MIM) structure is designed. A new freedom through tuning the thicknesses of each ring structures is introduced to realize a quasi-three-dimensional perfect absorber at three extinction wavelengths by using the finite difference time domain method. The physical machine is explained by the time domain field analyses and the coupled mode theory. The characteristics of the absorber make our proposed strategy applicable for the design of more general multiband and broadband perfect absorbers. In addition, these perfect absorbing metamaterials are found to exhibit excellent performance in refractive index sensing.

Plasmonic focusing of infrared SNOM tip patterned with asymmetric structures.

Several scattering type metal tips patterned with asymmetric metal/dielectric bump gratings are studied and proved to be efficient in focusing light energy into nano 'hot spot'. The dielectric bump tip shows complex mechanisms including local geometric resonance, surface plasmon polariton (SPP) standing wave resonance and Fano effect in the near-field enhancement. Additionally, considering the practical situation, we also demonstrate that, for the case of bending tip surface, the grating coupling method for plasmonic nano-focusing is still applicable if the intervals between neighboring bumps are well designed according to the surface bending curvature. With practical realizations, our results could benefit not only infrared scanning near-field optical microscopes (SNOMs) but also many other applications in nanotechnology such as sensing and lithography.