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The High-Order Variable-Coefficient Explicit-Implicit-Null Method for Diffusion and Dispersion Equations

应用数学与计算数学学报 2025年第1期7卷 115-150页

作者： Meiqi Tan Juan Cheng Chi-Wang Shu Graduate School China Academy of Engineering PhysicsBeijing 100088China Laboratory of Computational Physics Institute of Applied Physics and Computational MathematicsBeijing 100088China HEDPS Center for Applied Physics and TechnologyCollege of EngineeringPeking UniversityBeijing 100871China Division of Applied Mathematics Brown UniversityProvidenceRI 02912USA

For the high-order diffusion and dispersion equations,the general practice of the explicit-implicit-null(EIN)method is to add and subtract an appropriately large linear highest derivative term with a constant coefficient at one side of the equation,and then apply the standard implicit-explicit method to the equivalent *** call this approach the con-stant-coefficient EIN method in this paper and hereafter denote it by"CC-EIN".To reduce the error in the CC-EIN method,the variable-coefficient explicit-implicit-null(VC-EIN)method,which is obtained by adding and subtracting a linear highest derivative term with a variable coefficient,is proposed and studied in this *** with the local discon-tinuous Galerkin(LDG)spatial discretization,the VC-EIN method is shown to be uncon-ditionally stable and can achieve high order of accuracy for both one-dimensional and two-dimensional quasi-linear and nonlinear *** addition,although the computational cost slightly increases,the VC-EIN method can obtain more accurate results than the CC-EIN method,if the diffusion coefficient or the dispersion coefficient has a few high and narrow bumps and the bumps only account for a small part of the whole computational domain.

关键词： Diffusion equation Dispersion equation Stability Explicit-implicit-null(EIN)time discretization Local discontinuous Galerkin(LDG)method

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Bolstering functionality in multilayer and bilayer WS2 via focused laser micro-engraving

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Science China(Information Sciences) 2023年第6期66卷 94-101页

作者： Si Min CHAN Eng Tuan POH Jin Feng LEONG Kuan Eng Johnson GOH Chorng Haur SOW Department of Physics National University of Singapore Institute of Materials Research and Engineering Agency for ScienceTechnology and Research (A~*STAR) Division of Physics and Applied Physics School of Physical and Mathematical SciencesNanyang Technological University

Laser thinning of multilayer transition metal dichalcogenide(TMD)crystals has long been explored for its potential to produce localized domains of optically functional monolayers. Despite the high spatial control and resolution of the laser, the range of appropriate applications for these laser-thinned domains is still limited by the peripheral regions of unaltered thick multilayers. Herein, we report a newfound property of the laser-thinned regions to adhere strongly to the underlying substrate when lasered down to the monolayer limit. Upon a brief sonication in various solvents, the surrounding pristine multilayers can be lifted off, solely leaving behind the post-lasered monolayer patterns. Coupled with the flexible maneuver of the laser, various monolayer designs can be achieved, including micro-antenna, waveguide, and electrode geometries with lateral line widths at 1.5 μm resolution. Furthermore, we also detail the optical properties of the monolayers obtained from laser thinning, with those acquired from multilayers containing more defectbound excitons, whereas those lasered from bilayers presenting a trion-dominated profile similar to as-grown monolayers. Together, these findings allow for faster and more efficient multilayer removal and areal shaping of optically active monolayer domains, in comparison to multistep and complex standard lithographic etching(lithography–etch–develop)procedures.

关键词： WS$_2$ monolayer micro-patterning focused laser sonication lift-off

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A High Order Positivity-Preserving Discontinuous Galerkin Remapping Method Based on a Moving Mesh Solver for ALE Simulation of the Compressible Fluid Flow

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Communications in Computational physics 2023年第10期34卷 1177-1214页

作者： Xiaolu Gu Juan Cheng Chi-Wang Shu Graduate School China Academy of Engineering PhysicsBeijing 100088China Laboratory of Computational Physics Institute of Applied Physics and Computational MathematicsBeijing 100088China HEDPS Center for Applied Physics and Technologyand College of EngineeringPeking UniversityBeijing 100871China Division of Applied Mathematics Brown UniversityProvidenceRI 02912

The arbitrary Lagrangian-Eulerian(ALE)method is widely used in the field of compressible multi-material and multi-phase flow *** order to implement the indirect ALE approach for the simulation of compressible flow in the context of high order discontinuous Galerkin(DG)discretizations,we present a high order positivity-preserving DG remapping method based on a moving mesh solver in this *** remapping method is based on the ALE-DG method developed by Klingenberg et al.[17,18]to solve the trivial equation∂u/∂t=0 on a moving mesh,which is the old mesh before remapping at t=0 and is the new mesh after remapping at t=*** appropriate selection of the final pseudo-time T can always satisfy the relatively mild smoothness requirement(Lipschitz continuity)on the mesh movement velocity,which guarantees the high order accuracy of the remapping *** use a multi-resolution weighted essentially non-oscillatory(WENO)limiter which can keep the essentially non-oscillatory property near strong discontinuities while maintaining high order accuracy in smooth *** further employ an effective linear scaling limiter to preserve the positivity of the relevant physical variables without sacrificing conservation and the original high order *** experiments are provided to illustrate the high order accuracy,essentially non-oscillatory performance and positivity-preserving of our remapping *** addition,the performance of the ALE simulation based on the DG framework with our remapping algorithm is examined in one-and two-dimensional Euler equations.

关键词： Remapping discontinuous Galerkin method arbitrary Lagrangian-Eulerian high order accuracy multi-resolution WENO limiter positivity-preserving

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Predicting magnetic properties of van der Waals magnets using graph neural networks

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Physical Review Materials 2024年第11期8卷 114002页

作者： Peter Minch Romakanta Bhattarai Kamal Choudhary Trevor David Rhone Department of Physics Applied Physics and Astronomy Materials Science and Engineering Division

We study two-dimensional (2D) magnetic materials using state-of-the-art machine learning models that use a graph-theory framework. We find that representing materials as graphs allows us to better learn structure-property relationships by leveraging both the chemical properties of the constituent atoms and the connectivity between those atoms. Graph neural network models are capable of predicting global properties of crystal structure (i.e., graphwise properties) and local properties of the constituent atoms (i.e., nodewise properties). We embed physical constraints into our model by simultaneously making predictions of local and global properties. In particular, we use the atomistic line graph neural network (ALIGNN) architecture. We train the ALIGNN model on data comprising local and global magnetic moments of 314 2D structures of the form CrAiiBiBiiX6, based on monolayer Cr2Ge2Te6, calculated from first principles. By learning the relationships between both local and global magnetic properties, we demonstrate an improvement over models that only consider global magnetic properties.

关键词： Artificial neural networks Magnetic order 2-dimensional systems Magnetic thin films Convolutional neural networks High-throughput calculations

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Potassium ion doped manganese oxide nanoscrolls enhanced the performance of aqueous zinc-ion batteries

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Chinese Chemical Letters 2025年第1期36卷 549-555页

作者： Yang Li Xiaoxu Liu Tianyi Ji Man Zhang Xueru Yan Mengjie Yao Dawei Sheng Shaodong Li Peipei Ren Zexiang Shen Shaanxi Key Laboratory of Green Preparation and Functionalization for Inorganic Materials School of Material Science and EngineeringShaanxi University of Science and TechnologyXi’an 710021China Division of Physics and Applied Physics School of Physical and Mathematical SciencesNanyang Technological UniversitySingapore 637371Singapore

α-MnO_(2) is a potential positive electrode material for aqueous zinc-ion batteries,but its electrochemical performance of zinc storage requires further *** this paper,potassium ion-doped manganese dioxide nanoscrolls(K-MnO_(2))with oxygen vacancy were synthesized by a one-step hydrothermal *** was observed that the electrochemical specific capacity was 250.9 m Ah/g at a current density of 0.2 C,which was better than the existing commercialα-MnO_(2).At a high current of 1 C,these batteries demonstrate improved cycle *** radiation and other experiments as well as DFT theoretical calculations provided additional evidence that K doping was efficient in regulating the metal bond type and the mean charge regulation of covalent bonds with oxygen atoms in MnO_(2).When Mn-O and Mn-K bonds are present,K-MnO_(2) showed outstanding adsorption of Zn~(2+)and further enhanced the Zn^(2+)embedding ***,oxygen defects caused by doping boosted the development of the nanoscroll structure,leading to an increase in active sites available for electrochemical reactions and subsequently enhancing the electrical conductivity ofα-MnO_(2).This study exhibits the potential of optimizing materials based on manganese with the introduction of a potassium doping strategy,resulting in improved performance for aquatic zinc-ion batteries,and presents novel perspectives for related research.

关键词： Manganese dioxide K^(+) doping Nanoscrolls XAFS Aqueous zinc-ion batteries

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Nanoscale Electron Beam Patterning of PEDOT:PSS Free-Standing Films for Enhanced Thermoelectric Performance

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Energy & Environmental Materials 2025年第2期8卷 316-323页

作者： Hyejeong Lee Sunho Lee Sohyang Cha Gopinathan Anoop Hosun Shin Division of Chemical and Materials Metrology Korea Research Institute of Standards and Science KRISS Department of Aerospace Engineering University of Illinois at Urbana-Champaign Department of Applied Measurement Science University of Science and Technology UST Department of Physics Amrita Vishwa Vidyapeetham

The growing demand for flexible,lightweight,and highly processable electronic devices makes high-functionality conducting polymers such as poly(3,4-ethylene dioxythiophene):polystyrene sulfonate(PEDOT:PSS) an attractive alternative to conventional inorganic materials for various applications including ***,considerable improvements are necessary to make conducting polymers a commercially viable choice for thermoelectric *** study explores nanopatterning as an effective and unique strategy for enhancing polymer functionality to optimize thermoelectric parameters,such as electrical conductivity,Seebeck coefficient,and thermal *** nanopatterning into thermoelectric polymers is challenging due to intricate technical hurdles and the necessity for individually manipulating the interdependent thermoelectric ***,array nanopatterns with different pattern spacings are imposed on free-standing PEDOT:PSS films using direct electron beam irradiation,thereby achieving selective control of electrical and thermal transport in PEDOT:*** beam irradiation transformed PEDOT:PSS from a highly ordered quinoid to an amorphous benzoid *** pattern spacing resulted in a remarkable 70% reduction in thermal conductivity and a 60% increase in thermoelectric figure of merit compared to non-patterned PEDOT:*** proposed nanopatterning methodology demonstrates a skillful approach to precisely manipulate the thermoelectric parameters,thereby improving the thermoelectric performance of conducting polymers,and promising utilization in cutting-edge electronic applications.

关键词： nanotechnology polymers semiconductors thermoelectrics

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Controllable vortex lasing arrays in a geometrically frustrated exciton-polariton lattice at room temperature

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National Science Review 2023年第1期10卷 196-204页

作者： Jun Wang Yutian Peng Huawen Xu Jiangang Feng Yuqing Huang Jinqi Wu Timothy C.H.Liew Qihua Xiong Division of Physics and Applied Physics School of Physical and Mathematical Sciences Nanyang Technological University Department of Optical Science and Engineering and Shanghai Frontiers Science Research Base of Intelligent Optoelectronics and Perception Fudan University State Key Laboratory of Low-Dimensional Quantum Physics and Department of Physics Tsinghua University Beijing Academy of Quantum Information Sciences

Quantized vortices appearing in topological excitations of quantum phase transition play a pivotal role in strongly correlated physics involving the underlying confluence of superfluids,Bose-Einstein condensates and *** polaritons as bosonic quasiparticles have enabled studies of non-e quilibrium quantum gases and ***-polariton condensates in artificial lattices intuitively emulate energy-band structures and quantum many-body effects of condensed matter,underpinning constructing vortex lattices and controlling quantum fluidic ***,we harness exciton-polariton quantum fluids of light in a frustrated kagome lattice based on robust metal-halide perovskite microcavities,to demonstrate vortex lasing arrays and modulate their configurations at room *** energy-momentum spectra unambiguously reveal massless Dirac bands and quenched kinetic-energy flat bands coexisting in kagome lattices,where polariton condensates exhibit prototypical honeycomb and kagome spatial *** coherence investigations illustrate two types of phase textures of polariton condensates carrying ordered quantized-vortex arrays and π-phase shifts,which could be selected when needed using lasing emission *** findings offer a promising platform on which it is possible to study quantum-fluid correlations in complex polaritonic lattices and highlight feasible applications of structured light.

关键词： vortex lasing exciton–polariton lattice Bose–Einstein condensation the orbital angular momentum of light geometric frustration perovskite semiconductor

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Dimensionality-mediated type-II Dirac semimetal to quantum spin Hall insulator phase transition in TiC

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Physical Review B 2024年第11期110卷 115129页

作者： Ali Sufyan Hasan M. Abdullah J. Andreas Larsson Applied Physics Division of Materials Science Department of Engineering Sciences and Mathematics Department of Physics

We present first-principles results on monolayer (ML) and bulk titanium carbide (TiC) exhibiting dual topological characteristics: a quantum spin Hall insulator state in two-dimensional ML and a type-II Dirac semimetal state in its three-dimensional bulk form. The nontrivial nature of ML TiC is confirmed through the calculation of a Z2 invariant, spin Hall conductivity, and edge states. The edge band structure of ML TiC displays a single pair of gapless edge states at the M point. The insulating topological phase in ML TiC is driven by a band inversion around the M point involving Ti-d orbitals, with a nontrivial band gap of 0.47 eV. Our findings also indicate that ML TiC possesses excellent dynamical and thermal stability. Moreover, the bulk, ML hollow sphere arrays, and a 4-nm-thick film of TiC have already been synthesized, suggesting the high feasibility of the experimental synthesizing of ML TiC. On the other hand, we demonstrate that the bulk TiC hosts both a type-II Dirac cone and a topological nodal surface without spin-orbit coupling, protected by a combined symmetry of inversion and time reversal. The presence of spin-orbit coupling removes the nodal surface while preserving the type-II Dirac cone. Surface states connecting bulk Dirac nodes in bulk TiC can be readily observed, making the surface characteristics easily detectable in experiments.

关键词： Edge states Electronic structure First-principles calculations Topological materials

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Midgap states induced by Zeeman field and p-wave superconductor pairing

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Physical Review B 2024年第24期109卷 L241101-L241101页

作者： Yuanjun Jin XingYu Yue Yong Xu Xiang-Long Yu Guoqing Chang Guangdong Basic Research Center of Excellence for Structure and Fundamental Interactions of Matter Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials School of Physics Division of Physics and Applied Physics School of Physical and Mathematical Sciences Physics Department and Guangdong-Hong Kong Joint Laboratory of Quantum Matter the Institute of Micro/Nano Materials and Devices Shenzhen Institute for Quantum Science and Engineering International Quantum Academy Shenzhen 518048 China

The one-dimensional Su-Schrieffer-Heeger (SSH) model is central to band topology in condensed matter physics, which allows us to understand and design distinct topological states. In this work we find another mechanism to analogize the SSH model in a spinful system, realizing an obstructed atomic insulator by introducing intrinsic spin-orbit coupling and in-plane Zeeman field. In our model the midgap states originate from a quantized hidden polarization with invariant index Z2 (0; 01) due to the local inversion symmetry breaking. When the global inversion symmetry is broken, a charge pumping is designed by tuning the polarization. Moreover, by introducing the p+ip superconductor pairing potential, a topological phase dubbed obstructed superconductor (OSC) is identified. This new state is characterized by invariant index Z2 (0; 01) and nonchiral midgap states. More interestingly, these nonchiral edge states result in a chiral-like nonlocal conductance, which is different from the traditional chiral topological superconductor. Our findings not only find another strategy to achieve a spinful SSH model but also predict the existence of OSC, providing a promising avenue for further exploration of its transport properties.

关键词： 2-dimensional systems Electronic structure Node-line semimetals Topological insulators Topological materials Topological superconductors

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Element-specific high-bandwidth ferromagnetic resonance spectroscopy with a coherent extreme-ultraviolet source

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Physical Review applied 2024年第6期21卷 064047-064047页

作者： Michael Tanksalvala Anthony Kos Jacob Wisser Scott Diddams Hans T. Nembach Justin M. Shaw Applied Physics Division Time & Frequency Division Electrical Computer & Energy Engineering Department of Physics Physical Measurement Laboratory

In this paper, we apply a tabletop, ultrafast, high-harmonic generation (HHG) source to measure the element-specific ferromagnetic resonance (FMR) in ultrathin magnetic alloys and multilayers on an opaque Si substrate. We demonstrate a continuous-wave bandwidth up to 62 GHz, with a promise to extend it to 100 GHz or higher. This laboratory-scale instrument detects the FMR using ultrafast, extreme-ultraviolet (EUV) light, with photon energies spanning the M-edges of the most relevant magnetic elements. A radiofrequency frequency comb generator is used to produce a microwave excitation that is intrinsically synchronized to the EUV pulses with a timing jitter of 1.1 ps or better. We apply this system to measure the dynamics in a multilayer system as well as Ni-Fe and Co-Fe alloys. Since this instrument operates in reflection mode, it is a milestone toward measuring and imaging the dynamics of the magnetic state and spin transport of active devices on arbitrary substrates on a tabletop. The higher bandwidth also enables measurements of materials with high magnetic anisotropy, as well as ferrimagnets, antiferromagnets, and short-wavelength (high-wavevector) spin waves in nanostructures or nanodevices. Furthermore, the coherence and short wavelength of the EUV will enable extending these studies using dynamic nanoscale lensless imaging techniques such as coherent diffractive imaging, ptychography, and holography.

关键词： High-order harmonic generation Magnetization dynamics Magneto-optical Kerr effect Ultrafast phenomena Ferromagnetic resonance Optical nanoscopy Spectroscopy X-ray techniques

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