Cavity modes with optical orbital angular momentum in a metamaterial ring based on transformation optics

In this work, we theoretically study the cavity modes with transverse orbital angular momentum in metamaterial ring based on transformation optics. The metamaterial ring is designed to transform the straight trajectory of light into the circulating one by enlarging the azimuthal angle, effectively presenting the modes with transverse orbital angular momentum. The simulation results confirm the theoretical predictions, which state that the transverse orbital angular momentum of the mode not only depends on the frequency of the incident light, but also depends on the transformation scale of the azimuthal angle. Because energy dissipation inevitably reduces the field amplitude of the modes, the confined electromagnetic energy and the quality factor of the modes inside the ring are also studied in order to evaluate the stability of those cavity modes. The results show that the metamaterial ring can effectively confine light with a high quality factor and maintain steady modes with the orbital angular momentum, even if the dimension of the ring is much smaller than the wavelength of the incident light. This technique for exploiting the modes with optical transverse orbital angular momentum may provides a unique platform for applications related to micromanipulation.

Phononic frequency combs through nonlinear resonances

We explore an analogue of optical frequency combs in driven nonlinear phononic systems, and present a mechanism for generating phononic frequency combs through nonlinear resonances. In the underlying process, a set of phonon modes is simultaneously excited by the external driving which yields frequency combs with an array of discrete and equidistant spectral lines of each nonlinearly excited phonon mode. Frequency combs through nonlinear resonance of different orders are investigated, and in particular the possibility of correlation tailoring in higher-order cases is revealed. We suggest that our results can be applied in various nonlinear acoustic processes, such as phonon harvesting, and can also be generalized to other nonlinear systems.

Magnetic vortex core dynamics in correlated double plates of permalloy

In this work, we theoretically investigate the dynamics of magnetic vortex in a double-plate nanostructure, in which two square permalloy plates are joined together by imposing closely on a thin permalloy film. It is found that magnetic vortices have been formed in the two square permalloy plates. Due to the involving of the joint, the out-of-plane magnetization can also be observed at the sidewalls between the square plates and the joint area. The ground states with the vortex polarities (1,1) and (1,-1) are obtained when the thickness of the joint area is varied. By applying a short in-plane magnetic field pulse, the vortices deviate from their equilibrium positions and gyrate with damping radius. Interestingly, the vortex polarity can be switched if the strength of magnetic field approaches the threshold of switching field. Particularly by changing the strength of magnetic field, the two vortices can be switched alternatively in the double-plate nanostructure. The investigations may provide potential applications in magnetic vortex memories.

Spin-dependent energy bands and spin polarization in two-dimensional spin-orbit lateral superlattices

In this work, we theoretically investigate the spin-split energy bands of electrons and spin-polarized transport in two-dimensional (2D) spin-orbit lateral superlattices (SOLSLs), where the square rods with Rashba spin-orbit coupling (SOC) are distributed periodically by applying gate voltages on the semiconductor. Within the Landauer framework of ballistic transport, the energy bands, the electrical conductance, the spin polarization and the spin-dependent electronic charge distributions have been calculated. It is found that the energy minibands are formed and the energy levels are split up by the Rashba SOC. As a result, the spin-polarized conductance is obtained even in the absence of external magnetic fields and magnetic materials. Meanwhile, the spin polarization can approach high values in the SOLSLs by manipulating the strength of SOC. Furthermore, the spin-dependent electronic charge distributions have been obtained, which present a clear picture of spin-polarized conductance. Our investigations have the potential applications in spin-based quantum devices and semiconductor spintronics.

Multicavity x-ray Fabry-Perot resonance with ultrahigh resolution and contrast

Realization of x-ray Fabry-Perot (FP) resonance in back-Bragg-reflection crystal cavities has been proposed and explored for many years, but to date no satisfactory performance has been achieved. Here we show that single-cavity crystal resonators intrinsically have limited finesse and efficiency. To break this limit, we demonstrate that monolithic multicavity resonators with equal-width cavities and specific plate thickness ratios can generate ultrahigh-resolution FP resonance with high efficiency, steep peak tails, and ultrahigh contrast simultaneously. The resonance mechanism is similar to that of sequentially cascaded single-cavity resonators. The ultranarrow-bandwidth FP resonance is anticipated to have various applications, including modern ultrahigh-resolution or precision x-ray monochromatization, spectroscopy, coherence purification, coherent diffraction, phase contrast imaging, etc.

Multiple delocalization of electrons and persistent currents in random n-mer mesoscopic rings

We demonstrate that the electronic property of a mesoscopic ring can be alternatively tuned between metallic and insulative states by changing the Fermi level. The one-dimensional mesoscopic ring is constructed based on random n-mer model and threaded by magnetic flux. Multiple localization-delocalization transitions of electrons have been found. When the Fermi level approaches the resonant energy, persistent current approaches the behavior of free electrons regardless of the disorder, corresponding to the metallic feature. Away from the resonant state, the current is dramatically diminished, indicating an insulative feature. We suggest our results have potential application in designing quantum switch devices.

The coherence effect of surface plasmons on optical transmission in silver subwavelength hole arrays

We study the optical transmission through a silver film with subwavelength hole arrays, which is sandwiched by super-thin SiO2 layers. Based on finite-difference time-domain method, optical transmission and dispersion relation of surface plasmons are obtained. It is shown that surface plasmons are coherent in the top layer of the sandwich, which affects optical transmission in this subwavelength system. As a result, transmission modes can be tuned by changing the thickness of top layer. Resonant modes are also demonstrated by the electric field distribution. Besides, anti-resonances induced by Fano interference are also observed in this system. These properties may provide a peculiar approach to manipulate the propagation of electromagnetic wave in subwave-length microstructures.

Nanostructured copper filaments in electrochemical deposition

In this Letter we report a novel self-organized copper electrodeposition in an ultrathin layer of CuSO4 electrolyte. The macroscopic fingering branches of the deposit consist of long copper filaments covered with periodic corrugated nanostructures. The mechanism of the nanostructure formation is explored and the origin of the significant descent of the branching rate in electrodeposition is discussed. We suggest that this growth phenomenon provides deeper insights into the role of diffusion and migration on pattern formation in electrodeposition.

Intrinsic instability of the concentration field in diffusion-limited growth and its effect on crystallization

The dynamic behavior of the concentration field in crystallization is investigated by considering the coupling of the bulk concentration field and interfacial kinetics. It is shown that the concentration field may become unstable for perturbations with certain wavelength. When instability occurs, the physical environment in front of the growing interface will fluctuate and the interfacial growth mode will be affected accordingly. We suggest that our analysis can be used to interpret some spatial-temporal instabilities observed in crystallization.