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arXiv 2024年

作者： Ruta, Francesco L. Shao, Yinming Acharya, Swagata Mu, Anqi Jo, Na Hyun Ryu, Sae Hee Balatsky, Daria Pashov, Dimitar Kim, Brian S.Y. Katsnelson, Mikhail I. Analytis, James G. Rotenberg, Eli Millis, Andrew J. van Schilfgaarde, Mark Basov, D.N. Department of Physics Columbia University New York United States Department of Applied Physics and Applied Mathematics Columbia University New York United States National Renewable Energy Laboratory GoldenCO United States Advanced Light Source E.O. Lawrence Berkeley National Laboratory BerkeleyCA United States Department of Chemistry University of California BerkeleyCA United States Department of Physics University of California BerkeleyCA United States Theory and Simulation of Condensed Matter King’s College London London United Kingdom Department of Mechanical Engineering Columbia University New York United States Institute for Molecules and Materials Radboud University Nijmegen Netherlands Center for Computational Quantum Physics Flatiron Institute New York United States

Correlated materials may exhibit unusually high resistivity increasing linearly in temperature (1), breaking through the Mott-Ioffe-Regel bound, above which coherent quasiparticles are destroyed (2). The fate of collective charge excitations, or plasmons, in these systems is a subject of debate. Several studies suggest plasmons are overdamped (3-5) while others detect unrenormalized plasmons (6-8). Here, we present direct optical images of low-loss hyperbolic plasmon polaritons (HPPs) in the correlated van der Waals metal MoOCl2 (9). HPPs are plasmon-photon modes that waveguide through extremely anisotropic media (10-15), and are remarkably long-lived in MoOCl2. Many-body theory supported by photoemission results reveals that MoOCl2 is in an orbital-selective and highly incoherent Peierls phase. Different orbitals acquire markedly different bonding-antibonding character (16), producing a highly-anisotropic, isolated Fermi surface (17-18). The Fermi surface is further reconstructed and made partly incoherent by electronic interactions, renormalizing the plasma frequency. HPPs remain long-lived in spite of this, allowing us to uncover previously-unseen imprints of electronic correlations on plasmonic collective modes. © 2024, CC BY.

关键词： Van der Waals forces

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Multiple scales analysis of a nonlinear timestepping instability in simulations of solitons

arXiv

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arXiv 2024年

作者： Hyatt, Benjamin A. Lecoanet, Daniel Anders, Evan H. Burns, Keaton J. Department of Engineering Sciences and Applied Mathematics Northwestern University EvanstonIL60208 United States Center for Interdisciplinary Exploration and Research in Astrophysics Northwestern University EvanstonIL60201 United States Kavli Institute for Theoretical Physics University of California Santa Barbara Santa BarbaraCA93106 United States Department of Mathematics Massachusetts Institute of Technology CambridgeMA02139 United States Center for Computational Astrophysics Flatiron Institute New YorkNY10010 United States

The susceptibility of timestepping algorithms to numerical instabilities is an important consideration when simulating partial differential equations (PDEs). Here we identify and analyze a pernicious numerical instability arising in pseudospectral simulations of nonlinear wave propagation resulting in finite-time blow-up. The blow-up time scale is independent of the spatial resolution and spectral basis but sensitive to the timestepping scheme and the timestep size. The instability appears in multi-step and multi-stage implicit-explicit (IMEX) timestepping schemes of different orders of accuracy and has been found to manifest in simulations of soliton solutions of the Korteweg-de Vries (KdV) equation and traveling wave solutions of a nonlinear generalized Klein-Gordon equation. Focusing on the case of KdV solitons, we show that modal predictions from linear stability theory are unable to explain the instability because the spurious growth from linear dispersion is small and nonlinear sources of error growth converge too slowly in the limit of small timestep size. We then develop a novel multi-scale asymptotic framework that captures the slow, nonlinear accumulation of timestepping errors. The framework allows the solution to vary with respect to multiple time scales related to the timestep size and thus recovers the instability as a function of a slow time scale dictated by the order of accuracy of the timestepping scheme. We show that this approach correctly describes our simulations of solitons by making accurate predictions of the blow-up time scale and transient features of the instability. Our work demonstrates that studies of long-time simulations of nonlinear waves should exercise caution when validating their timestepping schemes. © 2024, CC BY-NC-ND.

关键词： Solitons

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Quantum embedding methods for correlated excited states of point defects: Case studies and challenges

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Physical Review B 2022年第23期105卷 235104-235104页

作者： Lukas Muechler Danis I. Badrtdinov Alexander Hampel Jennifer Cano Malte Rösner Cyrus E. Dreyer Center for Computational Quantum Physics Flatiron Institute 162 5th Avenue New York New York 10010 USA Theoretical Physics and Applied Mathematics Department Ural Federal University 620002 Yekaterinburg Russia Department of Physics and Astronomy Stony Brook University Stony Brook New York 11794-3800 USA Institute for Molecules and Materials Radboud University Heijendaalseweg 135 6525 AJ Nijmegen Netherlands

A quantitative description of the excited electronic states of point defects and impurities is crucial for understanding materials properties, and possible applications of defects in quantum technologies. This is a considerable challenge for computational methods, since Kohn-Sham density functional theory (DFT) is inherently a ground-state theory, while higher-level methods are often too computationally expensive for defect systems. Recently, embedding approaches have been applied that treat defect states with many-body methods, while using DFT to describe the bulk host material. We implement such an embedding method, based on Wannierization of defect orbitals and the constrained random-phase approximation approach, and perform systematic characterization of the method for three distinct systems with current technological relevance: a carbon dimer replacing a B and N pair in bulk hexagonal BN (CBCN), the negatively charged nitrogen-vacancy center in diamond (NV−), and an Fe impurity on the Al site in wurtzite AlN (FeAl). In the context of these test-case defects, we demonstrate that crucial considerations of the methodology include convergence of the bulk screening of the active-space Coulomb interaction, the choice of exchange-correlation functional for the initial DFT calculation, and the treatment of the “double-counting” correction. For CBCN we show that the embedding approach gives many-body states in agreement with analytical results on the Hubbard dimer model, which allows us to elucidate the effects of the DFT functional and double-counting correction. For the NV− center, our method demonstrates good quantitative agreement with experiments for the zero-phonon line of the triplet-triplet transition. Finally, we illustrate challenges associated with this method for determining the energies and orderings of the complex spin multiplets in FeAl.

关键词： First-principles calculations Nitrogen vacancy centers in diamond Point defects Wide band gap systems Density functional theory Exact diagonalization Wannier function methods

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Magnetic octupole moment of Yb173 using collinear laser spectroscopy

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Physical Review A 2021年第3期103卷 032826-032826页

作者： R. P. de Groote S. Kujanpää Á. Koszorús J. G. Li I. D. Moore Department of Physics University of Jyväskylä PB 35(YFL) FIN-40351 Jyväskylä Finland Department of Physics University of Liverpool Liverpool L69 7ZE United Kingdom Institute of Applied Physics and Computational Mathematics Beijing 100088 China

The hyperfine constants of the 4f146s6pP2o3 state in neutral Yb have been measured using three different dipole transitions. This state was recently shown to have a comparatively large hyperfine magnetic octupole splitting, and thus a puzzlingly large magnetic octupole moment. The measurement is performed using collinear laser spectroscopy on a fast atomic beam, which provides a straightforward route to probing long-lived metastable atomic states with high resolution. From the combined analysis of all three lines we find no significant evidence for a nonzero octupole moment in Yb173.

关键词： Fine & hyperfine structure Laser spectroscopy 150 ≤ A ≤ 189 Magnetic moment

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A self-induced mechanism of large-scale helical structures in compressible turbulent flows

arXiv

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arXiv 2024年

作者： Yan, Zheng Wang, Jianchun Wang, Lifeng Lei, Zhu Wu, Junfeng Duan, Junyi Tong, Fulin Li, Xinliang Yu, Changping Institute of Applied Physics and Computational Mathematics Beijing100094 China Department of Mechanics and Aerospace Engineering Southern University of Science and Technology Guangdong Shenzhen518055 China Center for Applied Physics and Technology HEDPS Peking University Beijing100871 China LHD Institute of Mechanics Chinese Academy of Sciences Beijing100190 China School of Engineering Science University of Chinese Academy of Sciences Beijing100049 China State Key Laboratory of Aerodynamics China Aerodynamics Research and Development Center Mianyang621000 China

A novel self-sustaining mechanism is proposed for large-scale helical structures in compressible turbulent flows. The existence of two channels of subgrid-scale and viscosity terms for large-scale helicity evolution is confirmed for the first time, through selecting a physical definition of the large-scale helicity in compressible turbulence. Under the influence of the fluid element expansion, it is found that the helicity is generated at small scales via the second-channel viscosity, and the inverse cross-scale helicity transfers at inertial scales through the second-channel helicity flux. Together, they form a self-induced mechanism, which provides a physical insight into the long-period characteristic of large-scale helical structures in the evolution of compressible flow systems. © 2024, CC0.

关键词： Turbulent flow

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Atomic Rydberg-state excitation in strong spatially inhomogeneous fields

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Physical Review A 2023年第3期107卷 033104-033104页

作者： Shilin Hu Xiaopeng Yi Li Guo Chengrui Bi Jing Chen Guangdong Provincial Key Laboratory of Quantum Metrology and Sensing & School of Physics and Astronomy Sun Yat-Sen University (Zhuhai Campus) Zhuhai 519082 China Institute of Applied Physics and Computational Mathematics P. O. Box 8090 Beijing 100088 China Department of Physics Shanghai Normal University Shanghai 200234 China Department of Modern Physics and Hefei National Research Center for Physical Sciences at the Microscale and School of Physical Sciences University of Science and Technology of China Hefei 230026 China Shenzhen Key Laboratory of Ultraintense Laser and Advanced Material Technology Center for Advanced Material Diagnostic Technology and College of Engineering Physics Shenzhen Technology University Shenzhen 518118 China

We investigated the Rydberg-state excitation process of a hydrogen atom subjected to spatially homogeneous and inhomogeneous laser fields by means of ab initio calculations. It is found that, comparing with atoms exposed to spatially homogeneous laser fields, the excitation probability decreases and the electron tends to occupy the states with lower principal quantum numbers and angular quantum numbers for atoms in spatially inhomogeneous laser pulses. Furthermore, calculations of a quantum model without taking into account ionization of the electron after it is coherently captured by the Rydberg state are inconsistent with the above-stated findings by ab initio calculations. Analysis indicates that the aforementioned intriguing features can be attributed to the enhanced ionization of the Rydberg states by inhomogeneous laser fields since the distributions of Rydberg states of high principal quantum numbers and angular quantum numbers locate far away from the core where the inhomogeneous electric fields become significant.

关键词： Atomic & molecular processes in external fields Electronic excitation & ionization Ultrafast phenomena Atoms Rydberg atoms & molecules Schroedinger equation

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Emergent conformal boundaries from finite-entanglement scaling in matrix product states

arXiv

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arXiv 2023年

作者： Huang, Rui-Zhen Zhang, Long Läuchli, Andreas M. Haegeman, Jutho Verstraete, Frank Vanderstraeten, Laurens Department of Physics and Astronomy University of Ghent Belgium Kavli Institute for Theoretical Sciences CAS Center for Excellence in Topological Quantum Computation University of Chinese Academy of Sciences Beijing100190 China Laboratory for Theoretical and Computational Physics Paul Scherrer Institute Villigen Switzerland Lausanne Switzerland Department of Applied Mathematics and Theoretical Physics University of Cambridge United Kingdom Center for Nonlinear Phenomena and Complex Systems Université Libre de Bruxelles Belgium

The use of finite entanglement scaling with matrix product states (MPS) has become a crucial tool for studying one-dimensional critical lattice theories, especially those with emergent conformal symmetry. We argue that finite entanglement introduces a relevant deformation in the critical theory. As a result, the bipartite entanglement Hamiltonian defined from the MPS can be understood as a boundary conformal field theory with a physical and an entanglement boundary. We are able to exploit the symmetry properties of the MPS to engineer the physical conformal boundary condition. The entanglement boundary, on the other hand, is related to the concrete lattice model and remains invariant under this relevant perturbation. Using critical lattice models described by the Ising, Potts, and free compact boson CFTs, we illustrate the influence of the symmetry and the relevant deformation on the conformal boundaries in the entanglement spectrum. Copyright © 2023, The Authors. All rights reserved.

关键词： Lattice theory

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Composite B-Spline Regularized Delta Functions for the Immersed Boundary Method: Divergence-Free Interpolation and Gradient-Preserving Force Spreading

arXiv

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arXiv 2024年

作者： Gruninger, Cole Griffith, Boyce E. Department of Mathematics University North Carolina Chapel HillNC United States Department of Applied Physical Sciences University of North Carolina Chapel HillNC United States Department of Biomedical Engineering University of North Carolina Chapel HillNC United States Carolina Center for Interdisciplinary Applied Mathematics University of North Carolina Chapel HillNC United States Computational Medicine Program University of North Carolina School of Medicine Chapel HillNC United States McAllister Heart Institute University of North Carolina School of Medicine Chapel HillNC United States

This paper presents an approach to enhance volume conservation in the immersed boundary (IB) method by employing regularized delta functions derived from composite B-splines. These delta functions are constructed using tensor product kernels, similar to the conventional IB method. However, the kernels are B-splines whose polynomial degree varies according to the normal and tangential directions of each velocity component. The conventional IB method, while effective for fluid-structure interaction applications, has long been challenged by poor volume conservation, particularly evident in simulations of pressurized, closed membranes. We demonstrate that composite B-spline regularized delta functions significantly enhance volume conservation through two complementary properties: they provide continuously divergence-free velocity interpolants and maintain the gradient character of forces corresponding to mean pressure jumps across interfaces. By correctly representing these forces as discrete gradients, they eliminate a key source of spurious flows that typically plague immersed boundary computations. Our approach maintains the local nature of the classical IB method, avoiding the computational overhead associated with the non-local Divergence-Free Immersed Boundary (DFIB) method’s construction of an explicit velocity potential which requires additional Poisson solves for interpolation and force spreading operations. Through a series of numerical experiments, we show that sufficiently regular composite B-spline kernels can maintain initial volumes to within machine precision. We provide a detailed analysis of the relationship between kernel regularity and the accuracy of force spreading and velocity interpolation operations. Our findings indicate that composite B-splines of at least C1 regularity produce results comparable to the DFIB method in dynamic simulations, with errors in volume conservation primarily dominated by truncation error of the employed time-stepping s

关键词： Delta functions

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Rayleigh-Taylor instability under multi-mode perturbation: discrete Boltzmann modeling with tracers

arXiv

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arXiv 2022年

作者： Li, Hanwei Xu, Aiguo Zhang, Ge Shan, Yiming Laboroatory of Computational Physics Institute of Applied Physics and Computational Mathematics Beijing100088 China Center for Applied Physics and Technology MOE Key Center for High Energy Density Physics Simulations College of Engineering Peking University Beijing100871 China State Key Laboratory of Explosion Science and Technology Beijing Institute of Technology Beijing100081 China Energy Resources Engineering Department Stanford University 367 Panama St StanfordCA94305-2220 United States

The Rayleigh-Taylor Instability (RTI) under multi-mode perturbation in compressible flow is probed via the Discrete Boltzmann Modeling (DBM) with tracers. The distribution of tracers provides clear boundaries between light and heavy fluids in the position space. Besides, the position-velocity phase space offers a new perspective for understanding the flow behavior of RTI with intuitive geometrical correspondence. The effects of viscosity, acceleration, compressibility, and Atwood number on the mixing of material and momentum and the mean non-equilibrium strength at the interfaces are investigated separately based on both the mixedness defined by the tracers and the non-equilibrium strength defined by the DBM. The mixedness increases with viscosity during early stage but decreases with viscosity at the later stage. Acceleration, compressibility, and Atwood number show enhancement effects on mixing based on different mechanisms. After the system relaxes from the initial state, the mean non-equilibrium strength at the interfaces presents an initially increasing and then declining trend, which is jointly determined by the interface length and the macroscopic physical quantity gradient. We conclude that the four factors investigated all significantly affect early evolution behavior of RTI system, such as the competition between interface length and macroscopic physical quantity gradient. The results contribute to the understanding of the multi-mode RTI evolutionary mechanism and the accompanied kinetic effects. © 2022, CC BY-NC-ND.

关键词： Interface states

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Scaling limits of external multi-particle DLA on the plane and the supercooled stefan problem

arXiv

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arXiv 2021年

作者： Nadtochiy, Sergey Shkolnikov, Mykhaylo Zhang, Xiling Department of Applied Mathematics Illinois Institute of Technology ChicagoIL60616 United States ORFE Department Bendheim Center for Finance Program in Applied & Computational Mathematics Princeton University PrincetonNJ08544 United States

We consider (a variant of) the external multi-particle diffusion-limited aggregation (MDLA) process of Rosenstock and Marquardt on the plane. Based on the recent findings of [11], [10] in one space dimension it is natural to conjecture that the scaling limit of the growing aggregate in such a model is given by the growing solid phase in a suitable "probabilistic" formulation of the single-phase supercooled Stefan problem for the heat equation. To address this conjecture, we extend the probabilistic formulation from [10] to multiple space dimensions. We then show that the equation that characterizes the growth rate of the solid phase in the supercooled Stefan problem is satisfied by the scaling limit of the external MDLA process with an inequality, which can be strict in general. In the course of the proof, we establish two additional results interesting in their own right: (i) the stability of a "crossing property" of planar Brownian motion and (ii) a rigorous connection between the probabilistic solutions to the supercooled Stefan problem and its classical and weak *** Codes 82C22, 80A22, 60H30 Copyright © 2021, The Authors. All rights reserved.

关键词： Supercooling

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