Magnetic exchange field has been demonstrated to be effective in enhancing the valley splitting of monolayer transition-metal dichalcogenides experimentally. However, how magnetic exchange coupling affects the magnetooptical behaviors in massive Dirac systems remains elusive. Using k⃗·p⃗ model and Kubo formula, we theoretically report that optical Hall conductivity and giant magnetooptical effects can be induced in monolayer transition-metal dichalcogenides even if there is no any magnetic field involved when considering magnetic exchange interaction. Such an unusual result originates from the fact that the existence of magnetic exchange coupling effectively enables the breaking of time reversal symmetry, which grants the removal of valley degeneracy and unveils the possibility of generation and manipulation of magnetooptical effects in monolayer transition-metal dichalcogenides with no need for magnetic field. Our results suggest that the presence of magnetic exchange coupling of transition-metal dichalcogenides represents an alternative strategy capable of inducing magnetoopitcal effects, which can be extended to other monolayer massive Dirac systems.
A p-n junction photoanode has been fabricated by depositing p-type NiO nanoparticles on the n-type hematite thin film. Such a photoanode is employed for a photoelectrochemical cell. NiO not only facilitates the extraction of accumulated holes from hematite via the p-n junction, but also lowers the barrier for oxygen evolution reaction.
Color tuning is a fascinating and indispensable property in applications such as advanced display, active camouflaging and information encryption. Thus far, a variety of reconfigurable approaches have been implemented to achieve color change. However, it is still a challenge to enable a continuous color tuning over the entire hue range in a simple, stable and rapid manner without changes in configuration and material properties. Here, we demonstrate an all-optical continuously tunable plasmonic pixel scheme via a modular design approach to realize polarization-controlled full color tuning by breaking the intrinsic symmetry of the unit cell layout. The polarization-controlled full color tunable plasmonic pixels consist of three different types of color modules oriented at an angle of 60{\deg} with respect to each other, corresponding to three subtractive primary colors. Without changing the structural properties or surrounding environment, the structural colors can be continuously and precisely tuned across all hues by illuminating linearly polarized light with different polarization directions. Meanwhile, the plasmonic pixels can be flexibly customized for various color tuning processes, such as different initial output colors and color tuning sequences, through the appropriate choice of component modules and the elaborate design of module layouts. Furthermore, we extend the color tuning to achromatic colors, white or black, with the utilization of a single module or the introduction of a black module. The proposed polarization-controlled full color tunable plasmonic pixels hold considerable potential to function as next-generation color pixels integrated with liquid-crystal polarizers.
Micro-motors driven by light field have attracted much attentions for their potential applications. In order to drive the rotation of a micro-motor, structured optical beams with orbital angular momentum, spin angular momentum, anisotropic medium, and/or inhomogeneous intensity distribution should be used. Even though, it is still challenge to increase the optical torques (OT) in a flexible and controllable way in case of moderate incident power. In this paper, a new scheme achieving giant optical torque is proposed by increasing both the force arm and the force amplitude with the assistance of a ring resonator. In this case, the optical torque doesn't act on the target directly by the incident beam, but is transmitted to it by rotating the ring resonator connected with it. Using the finite-difference in time-domain method, we calculate the optical torque and find that both the direction and the amplitude of the torque can be tuned flexibly by modifying the frequency, or the relative phases of the sources. More importantly, the optical torque obtained here by linearly polarized beams can be 3 orders larger than those obtained using the structured beams. This opt-mechanical-resonator based optical torque engineering system may find potential applications in optical driven micro-machines.
An infrared dual-band perfect absorber based on asymmetric T-shaped plasmonic array is designed and numerically investigated. Two distinct absorption peaks are achieved by localized surface plasmon polariton (LSPP) mode over a wide incident angular range. Both the absorption peaks can be finely tuned independently by varying the geometry of the structure. In our proposed structure, the period of the T-shaped structures becomes less and the multiple LSPP peaks are suppressed, which result in the sideband of absorption peaks very low. This dual-band perfect absorber has potential applications such as in infrared imaging devices, thermal bolometers, and wavelength selective radiators.
Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.
A new microelectromechanical system (MEMS)-based tensile testing stage (with integrated actuator, direct load sensing beam, and electrodes for controlled assembly of an individual nanostructure) was developed and used for in situ tensile loading of a templated carbon nanotube (T-CNT) inside a scanning electron microscope (SEM). Specifically, an increasing tensile load was applied to the T-CNT by actuating the device and high-resolution scanning electron microscopy images were acquired at different loads. The load (from the bending of the direct force-sensing beam), the elongation of the specimen during loading, and the specimen geometry were all obtained from analysis of SEM images. The stress versus strain curve and Young’s modulus were thus obtained. A model is presented for the tensile loading experiment, and the fit value of Young’s modulus from this model is compared to values obtained by an independent method. The results of this experiment on a T-CNT suggest the use of this device for loading other nanostructures and also for designing other MEMS-based systems, such as a compressive testing stage.
We perform a comprehensive analysis of multi-band absorption by exciting magnetic polaritons in the infrared region. According to the independent properties of the magnetic polaritons, we propose a parallel inductance and capacitance(PLC) circuit model to explain and predict the multi-band resonant absorption peaks, which is fully validated by using the multi-sized structure with identical dielectric spacing layer and the multilayer structure with the same strip width. More importantly, we present the application of the PLC circuit model to preliminarily design a radiative cooling structure realized by merging several close peaks together. This omnidirectional and polarization insensitive structure is a good candidate for radiative cooling application.
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