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Valley filtering in 8-Pmmn borophene based on an electrostatic waveguide constriction

Physical Review B 2024年第20期109卷 205413-205413页

作者： Emile Vanderstraeten Dries Vande Ginste quest IDLab Department of Information Technology Ghent University/imec Technologiepark-Zwijnaarde 126 9000 Ghent Belgium

Materials with tilted Dirac cones, such as 8−Pmmn borophene, are being explored for valleytronic applications as the tilting direction is different for nonequivalent valleys. In this paper, a valley-filtering device based on electrostatic waveguides is proposed. First, these waveguides are examined from a theoretical point of view. An inner product is defined starting from the probability current density along the waveguide axis. It is shown that the bound modes with real eigenvalues are mutually orthogonal and orthogonal with respect to all radiating modes. In a next step, by exploiting these orthogonality properties, a simulation procedure is introduced based on an explicit, symplectic partitioned Runge-Kutta time-stepping method specifically adapted for this problem. Finally, this approach is applied to the situation of a waveguide nanoconstriction and it is demonstrated that this structure can function as a valley filter. Within a certain window in the energy domain, transmission is practically zero for one valley, while being almost perfect for the other one. The effect of several design variables, such as length and width of the constriction, is carefully investigated. Moreover, the effect of misalignment between the tilting direction and the waveguide axis is assessed, showing that the proposed valley-filtering design is robust against deviations up to several tens of degrees. In addition, the simulation results reveal that the dispersion relation of the waveguide modes is not necessarily monotonic, which can give rise to oscillations in the transmission function due to interference effects.

关键词： Valleytronics Quantum wires Two-dimensional electron system finite-difference time-domain method

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Magnonic bandgap openings and in-gap propagating states in domain-wall waveguides induced by periodic modulations

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Physical Review B 2024年第18期109卷 184401-184401页

作者： Qiyun Yi Zhenhua Tang Daoyun Zhu Xiangjun Xing Wei Zhang Yan Zhou School of Physics and Optoelectronic Engineering Guangdong University of Technology Guangzhou 510006 China Guangdong Provincial Key Laboratory of Information Photonics Technology Guangdong University of Technology Guangzhou 510006 China Experimental Teaching Department Guangdong University of Technology Guangzhou 510006 China School of Science and Engineering The Chinese University of Hong Kong Shenzhen Guangdong 518172 China

Magnonic waveguides based on magnetic domain walls surpass conventional magnonic waveguides, which typically feature single magnetic domains, in nearly all critical aspects. Consequently, they are considered pivotal for the development of future nanomagnonic circuits. A distinctive feature of these waveguides is the complete absence of a bandgap, known as the vanishing magnon barrier. This feature is of great theoretical importance and has practical relevance for several applications, but it has received limited attention thus far. In our research, we employ micromagnetic simulations to investigate the spin-wave propagation in a domain-wall based magnonic waveguide, which includes reconfigurable periodic modulations. The magnonic band structure within the domain-wall waveguide can be significantly altered based on the magnetization configuration of the modulating magnets, resulting in the creation of bandgaps or leaving the structure unchanged, as though no modulation were applied. The bandgaps arise from the Bragg reflection of spin waves due to an induced periodic potential. A resonance-enhanced propagation state of the waveguide and modulation magnets, indicative of mode matching, results in the emergence of an allowed band within each bandgap under specific conditions. This study may open an effective route to control the band structure of domain-wall waveguides.

关键词： domain walls Micromagnetism Spin waves Multilayer thin films Nanowires finite-difference time-domain method Landau-Lifschitz-Gilbert equation Micromagnetic modeling

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Completion of model validation experiments at the Princeton starshade testbed

Completion of model validation experiments at the Princeton ...

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Conference on Space Telescopes and Instrumentation - Optical, Infrared, and Millimeter Wave

作者： Shaklan, Stuart Harness, Anthony Kasdin, N. Jeremy Galvin, Michael Balasubramanian, K. White, Victor Yee, Karl Muller, Richard Willems, Phillip Dumont, Philip Vuong, Simon Lisman, Doug CALTECH Jet Prop Lab 4800 Oak Grove Dr Pasadena CA 91109 USA Princeton Univ Dept Mech & Aerosp Engn Princeton NJ 08544 USA

ISBN: (纸本)9781510653429

Following the results of Starshade Milestone 1 in which we demonstrated broadband contrast better than 10-10, we have performed model validation experiments to show that diffraction models accurately predict the contrast due to perturbations representing the building blocks of the instrument error budget. The perturbations include the displacement of petal edge segments, sinusoidal petal edge shape deformations, global petal position errors, and random petal radial placement errors. We also show that the model accurately predicts the combined effects of two errors. The experiments result in a measured Model Uncertainty Factor (MUF) that is then applied to the starshade instrument contrast error budget.

关键词： Diffraction Data modeling Photomasks Polarization Telescopes Manufacturing Etching Error analysis finite-difference time-domain method Optical instrument design

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Submillimeter-Wave Multiphase Oscillation Using Traveling Pulses in a Resonant-Tunneling Diode-Oscillator Lattice

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JOURNAL OF INFRARED MILLIMETER AND TERAHERTZ WAVES 2021年第4期42卷 426-445页

作者： Sawai, Shinya Narahara, Koichi Kanagawa Inst Technol Dept Elect & Elect Engn 1030 Shimoogino Atsugi Kanagawa 2430292 Japan

We recently proposed a multiphase oscillator utilizing a periodic pulse train generated and propagated in a closed one-dimensional lattice of resonant-tunneling diode (RTD) oscillators, each of which establishes the neighbor-to-neighbor coupling through lossy inductors. In this work, we develop the design criteria for the bias dependence of oscillation frequency through the bifurcation analysis based on the quasi-continuous model of the lattice. We then model the lattice in the full-wave scheme using the finite-difference time-domain method and validate the multiphase oscillation in submillimeter-wave frequencies. Finally, several experimental observations conducted in MHz frequencies using tunnel diodes in place of RTDs are presented to validate several synchronization properties of the pulse train in the lattice including the direction-specified transmission of pulse train and its application to the multiphase oscillator.

关键词： Resonant-tunneling diodes finite-difference time-domain method Bifurcation Multiphase oscillation Voltage-controlled oscillation Self-injection locking

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Compact Matrix-Exponential-Based FDTD with Second-Order PML and Direct Z-Transform for Modeling Complex Subsurface Sensing and Imaging Problems

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REMOTE SENSING 2021年第1期13卷 1-12页

作者： Feng, Naixing Zhang, Yuxian Wang, Guo Ping Zeng, Qingsheng Joines, William T. Shenzhen Univ Inst Microscale Optoelect Shenzhen 518060 Peoples R China Nanjing Univ Aeronaut & Astronaut Coll Astronaut Nanjing 210016 Peoples R China Duke Univ Dept Elect & Comp Engn Durham NC 27708 USA

To simulate complex subsurface sensing and imaging problems with both propagating and evanescent waves by the finite-difference time-domain (FDTD) method, the highly-accurate second-order perfectly matched layer (SO-PML) formulations based on the direct Z-transform (DZT) and the matrix exponential (ME) techniques are compactly and efficiently proposed for modeling open-domain problems. During mathematical deductions, several manipulations, for example, convolution computations, formulation reorganizations, or variable substitutions, can be circumvented due to the fact that the ME-based method shows a compact first-order differential matrix form. Besides, any material attributes can be completely circumvented because of using electric and magnetic flux densities, consequently, the proposed DZT-SO-PML could be applied without needing any alteration. Moreover, the DZT-SO-PML method can not only preserve better absorption accuracies, but also attain palpable improvements in computational efficiencies, even if the distance between the DSP-SO-PML truncation and the target becomes closer for modeling 3D open-domain subsurface sensing and imaging problems. Finally, numerical examples have been carried out to illustrate and validate these proposed formulations.

关键词： direct Z-transform method finite-difference time-domain method matrix exponential subsurface sensing and imaging second-order perfectly matched layer

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An alternative amelioration of ME-based DZT-PML for truncating FDTD problems

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ELECTROMAGNETICS 2021年第2期41卷 83-97页

作者： Feng, Naixing Li, Xue-Shi Zhang, Yuxian Sun, Yanming Shenzhen Univ Inst Microscale Optoelect Shenzhen Peoples R China Guangdong Univ Technol Sch Automat Guangzhou 510006 Peoples R China

In order to further alleviate computational burdens and enhance accuracies, we propose an efficient amelioration on the complex-frequency-shifted perfectly matched layer (CFS- PML) via introducing both direct Z-transform (DZT) and matrix exponential (ME) methods for terminating the finite-difference time-domain (FDTD) region. The method is here referred as the DZT-ME-PML. Due to introducing the DZT method, the proposal can avoid the disadvantages of approximate bilinear and matched Z-transform in modeling fine and course structures, leading to achieving higher accuracies. Moreover, by employing the ME technique, the proposal develops into the compact first-order differential matrix form applied to evading the convolution manipulations, the variable replacements, and the formulation rearrangements during the mathematical derivations. Besides, the proposed DZT-ME-PML can not only flexibly terminate the arbitrary media when adding the DB constitutive relation, but efficiently attenuate evanescent waves, and reduce the late-time reflections due to the CFS scheme. Three-dimensional (3D) numerical examples have been carried out to illustrate the validity and accuracy of the proposed DZT-ME-PML. Eventually, applied to solving geophysical problem with the very low frequency (VLF) case, the DZT-ME-PML shows stronger absorption accuracy than the general ME-PML method.

关键词： Complex-frequency-shifted perfectly matched layer direct Z-transform finite-difference time-domain method matrix exponential very low frequency

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Rotationally displaced electric field intensity distribution around square nanoantennas induced by circularly polarized light

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Physical Review B 2024年第3期109卷 035428-035428页

作者： Naoki Ichiji Takuya Ishida Ikki Morichika Tetsu Tatsuma Satoshi Ashihara Institute of Industrial Science The University of Tokyo 4-6-1 Komaba Meguro-Ku Tokyo 153-8505 Japan

An optical field around regular polygon metal nanostructures excited by circularly polarized light can exhibit rotationally displaced intensity distributions. Although this phenomenon has been recognized, its underlying mechanisms have not been sufficiently explained. Herein, finite-difference time-domain simulations and model analyses reveal that the rotationally displaced optical intensity distribution can be generated when each of the linear polarization components that constitute circular polarization excites a superposition of multiple modes. The proposed model reasonably explains the rotationally displaced patterns for a square nanoantenna and other regular-polygon nanoantennas.

关键词： Electric polarization Nano-oscillators Plasmons finite-difference time-domain method

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Light-matter interaction at rough surfaces: A morphological perspective on laser-induced periodic surface structures

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Physical Review B 2024年第11期110卷 115438页

作者： Vladimir Yu. Fedorov Jean-Philippe Colombier Université Jean Monnet Saint-Etienne CNRS IOGS Laboratoire Hubert Curien UMR 5516 Saint-Etienne F-42023 France

We use ab initio electromagnetic simulations to investigate light absorption by rough surfaces in the context of the formation of laser-induced periodic surface structures. Our approach involves modeling a rough surface using a statistical description of its continuous height distribution via a corresponding correlation function. We study the influence of incident light polarization and various statistical properties of surface roughness, such as root-mean-square height and correlation length, on the distribution of absorbed laser energy. By analyzing light absorption in different layers of the surface selvedge, we elucidate how different features of surface morphology influence the shape of the resulting periodic surface structures. We show that circularly polarized laser pulses are highly sensitive to initial or progressively developing asymmetries in surface roughness.

关键词： Light-matter interaction Optical interactions with surfaces Roughness Ultrafast phenomena finite-difference time-domain method Maxwell's equations

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Localized surface plasmons in disk supershape shell nanoparticles

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2025年第6期42卷 1366-1376页

作者： Hashemi, Parivash Yaghooti, Emadoddin Babaei, Ferydon Univ Qom Dept Phys Qom Iran

Here, we reported the excitation of multiple localized surface plasmons in disk supershape shell nanoparticles using the finite difference time domain method. All plasmon bands of disk supershape shell nanoparticles were extracted from extinction spectra. The characteristics of the plasmon bands were investigated as functions of the structural parameters of the shell nanoparticles and the refractive indices of the environment and substrate. The obtained results showed in general, two types of plasmon bands appear, one at longer wavelengths and the other at shorter wavelengths, which are, respectively, dependent on the excitation of dipoles and higher-order multipoles. The patterns of the electric field and charge distribution prove these points. The Purcell factor spectra revealed that the resonant modes corresponding to plasmonic bands occur in the emission spectra, although new modes appear between them due to the asymmetry of the nanoparticle geometry. This study could potentially have applications in sensors, thermal photonics, and energy harvesting. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

关键词： finite-difference time-domain method Localized surface plasmon resonance Localized surface plasmons Metal nanoparticles Resonant modes Solar cell efficiency

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Tunable narrowband perfect absorption and active phase transition driven by gain-coupled bound states in the continuum: A basis for sensing

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Physical Review Applied 2024年第5期22卷 054002页

作者： Xiao Wang Huachun Zhu Te Ji Weiwei Peng Hongwei Zhao Maoxiong Zhao Lei Shi Min Chen Jie Wang Shanghai 201800 China Shanghai Synchrotron Radiation Facility Beijing 100049 China State Key Laboratory of Surface Physics and Department of Physics

Plasmonic nanostructures provide an excellent platform for tailoring the light-matter interaction, and have found applications ranging from perfect absorption to phase modulation. However, realizing narrowband perfect plasmonic absorbers and dynamical control of light response remains challenging, primarily due to the high intrinsic losses and the limited tunability of metallic components. Here, a gain-coupled-bound state in the continuum (BIC) strategy is proposed to achieve a narrowband perfect plasmonic absorber with tailored functionality. The bandwidth can be dramatically reduced, with quadratic scalability dependence on the perturbation parameters of the quasi-BIC, essentially arising from the powerful physics of BIC in radiation engineering. Moreover, this strategy can make the reflection phase of the plasmonic absorber undergo across a full phase diagram. In particular, it displays functional phase transitions upon crossing the critical coupling or lasing during tailoring loss by gain. This phase transition is further utilized to realize a highly sensitive phase interrogation refractometric sensor. This work provides a profound physical insight into the tailoring functionalities of absorption and phase response, and may open up possibilities for trace detection in biochemical and chemical analysis.

关键词： Analytical chemistry Bound states in the continuum Light propagation, transmission & absorption Photonics Plasmonics Metasurfaces Coupled mode theory finite-difference time-domain method

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