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Machine learning techniques to construct detailed phase diagrams for skyrmion systems

Physical Review B 2022年第21期105卷 214423-214423页

作者： F. A. Gómez Albarracín H. D. Rosales Instituto de Física de Líquidos y Sistemas Biológicos (IFLYSIB) UNLP-CONICET Facultad de Ciencias Exactas La Plata Argentina Departamento de Física Facultad de Ciencias Exactas Universidad Nacional de La Plata La Plata Argentina and Departamento de Ciencias Básicas Facultad de Ingeniería Universidad Nacional de La Plata La Plata Argentina

Recently, there has been an increased interest in the application of machine learning (ML) techniques to a variety of problems in condensed-matter physics. In this regard, of particular significance is the characterization of simple and complex phases of matter. Here, we use a ML approach to construct the full phase diagram of a well-known spin model combining ferromagnetic exchange and Dzyaloshinskii-Moriya (DM) interactions where topological phases emerge. At low temperatures, the system is tuned from a spiral phase to a skyrmion crystal by a magnetic field. However, thermal fluctuations induce two types of intermediate phases, bimerons and skyrmion gas, which are not as easily determined as spirals or skyrmion crystals. We resort to large-scale Monte Carlo simulations to obtain low-temperature spin configurations and train a convolutional neural network (CNN), taking only snapshots at specific values of the DM couplings, to classify between the different phases, focusing on the intermediate and intricate topological textures. We then apply the CNN to higher-temperature configurations and to other DM values to construct a detailed magnetic-field–temperature phase diagram, achieving outstanding results. We discuss the importance of including the disordered paramagnetic phases in order to get the phase boundaries, and, finally, we compare our approach with other ML algorithms.

关键词： Dzyaloshinskii-Moriya interaction Ferromagnetism Magnetism Skyrmions Machine learning metropolis algorithm Monte Carlo methods

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Thermodynamic properties of argon from Monte Carlo simulations using ab initio potentials

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Physical Review E 2022年第6期105卷 064129-064129页

作者： Philipp Ströker Robert Hellmann Karsten Meier Institut für Thermodynamik Helmut-Schmidt-Universität/Universität der Bundeswehr Hamburg Holstenhofweg 85 22043 Hamburg Germany

Ten different thermodynamic properties of the noble gas argon in the liquid and supercritical regions were obtained from semiclassical Monte Carlo simulations in the isothermal-isobaric ensemble using ab initio potentials for the two-body and nonadditive three-body interactions. Our results for the density and speed of sound agree with the most accurate experimental data for argon almost within the uncertainty of these data, a level of agreement unprecedented for many-particle simulations. This demonstrates the high predictive but yet unexploited power of ab initio potentials in the field of molecular modeling and simulation for thermodynamic properties of fluids.

关键词： Classical statistical mechanics Equations of state Thermal properties metropolis algorithm

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A Bayesian approach to determine the composition of heterogeneous cancer tissue

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BMC BIOINFORMATICS 2018年第3-Sup期19卷 90-90页

作者： Katiyar, Ashish Mohanty, Anwoy Hua, Jianping Chao, Sima Lopes, Rosana Datta, Aniruddha Bittner, Michael L. Texas A&M Univ Dept Elect & Comp Engn College Stn TX 77843 USA Brigham & Womens Hosp Div Genet Dept Med POB 1212 Boston MA 02115 USA Harvard Med Sch POB 1212 Boston MA 02115 USA Texas A&M Univ Ctr Bioinformat & Genom Syst Engn TEES College Stn TX 77843 USA Translat Genom Res Inst Phoenix AZ USA

Background: Cancer Tissue Heterogeneity is an important consideration in cancer research as it can give insights into the causes and progression of cancer. It is known to play a significant role in cancer cell survival, growth and metastasis. Determining the compositional breakup of a heterogeneous cancer tissue can also help address the therapeutic challenges posed by heterogeneity. This necessitates a low cost, scalable algorithm to address the challenge of accurate estimation of the composition of a heterogeneous cancer tissue. Methods: In this paper, we propose an algorithm to tackle this problem by utilizing the data of accurate, but high cost, single cell line cell-by-cell observation methods in low cost aggregate observation method for heterogeneous cancer cell mixtures to obtain their composition in a Bayesian framework. Results: The algorithm is analyzed and validated using synthetic data and experimental data. The experimental data is obtained from mixtures of three separate human cancer cell lines, HCT116 (Colorectal carcinoma), A2058 (Melanoma) and SW480 (Colorectal carcinoma). Conclusion: The algorithm provides a low cost framework to determine the composition of heterogeneous cancer tissue which is a crucial aspect in cancer research.

关键词： Cancer tissue heterogeneity Bayesian modeling metropolis algorithm Kernel density estimation

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Optical Kinetic Theory of Nonlinear Multimode Photonic Networks

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Physical Review Letters 2024年第19期132卷 193802-193802页

作者： Arkady Kurnosov Lucas J. Fernández-Alcázar Alba Ramos Boris Shapiro Tsampikos Kottos Department of Physics Wave Transport in Complex Systems Laboratory Wesleyan University Middletown Connecticut 06459 USA Institute for Modeling and Innovative Technology IMIT (CONICET - UNNE) Corrientes W3404AAS Argentina Physics Department Natural and Exact Science Faculty Northeastern University of Argentina Corrientes W3404AAS Argentina Technion - Israel Institute of Technology Technion City Haifa 3200 Israel

Recent experimental developments in multimode nonlinear photonic circuits (MMNPCs), have motivated the development of an optical thermodynamic theory that describes the equilibrium properties of an initial beam excitation. However, a nonequilibrium transport theory for these systems, when they are in contact with thermal reservoirs, is still terra incognita. Here, by combining Landauer and kinematics formalisms we develop a universal one-parameter scaling theory that describes the whole transport behavior from the ballistic to the diffusive regime, including both positive and negative optical temperature scenarios. We also derive a photonic version of the Wiedemann-Franz law that connects the thermal and power conductivities. Our work paves the way toward a fundamental understanding of the transport properties of MMNPCs and may be useful for the design of all-optical cooling protocols.

关键词： Classical optics Kinetic theory Nonequilibrium & irreversible thermodynamics Nonlinear optics Optics & lasers Transport phenomena Nonequilibrium lattice models Nonequilibrium systems Optical fibers Waveguides Data analysis Finite-size scaling Linear response theory metropolis algorithm Monte Carlo methods Scaling methods Schroedinger equation

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Quantum many-body scars with chiral topological order in two dimensions and critical properties in one dimension

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Physical Review B 2020年第23期102卷 235106-235106页

作者： N. S. Srivatsa Julia Wildeboer Alexander Seidel Anne E. B. Nielsen Max-Planck-Institut für Physik komplexer Systeme D-01187 Dresden Germany Department of Physics Arizona State University Tempe Arizona 85287 USA Department of Physics Washington University in St. Louis St. Louis Missouri 63130 USA

We construct few-body, interacting, nonlocal Hamiltonians with a quantum scar state in an otherwise thermalizing many-body spectrum. In one dimension, the embedded state is a critical state, and in two dimensions, the embedded state is a chiral topologically ordered state. The models are defined on slightly disordered lattices, and the scar state appears to be independent of the precise realization of the disorder. A parameter allows the scar state to be placed at any position in the spectrum. We show that the level spacing distributions are Wigner-Dyson and that the entanglement entropies of the states in the middle of the spectrum are close to the Page value. Finally, we confirm the topological order in the scar state by showing that one can insert anyons into the state.

关键词： Anyons Quantum scars Topological phases of matter Strongly correlated systems Conformal field theory Exact diagonalization metropolis algorithm

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Approximate dynamical eigenmodes of the Ising model with local spin-exchange moves

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Physical Review E 2019年第1期100卷 012132-012132页

作者： Wei Zhong Debabrata Panja Gerard T. Barkema Department of Information and Computing Sciences Utrecht University Princetonplein 5 3584 CC Utrecht the Netherlands

We establish that the Fourier modes of the magnetization serve as the dynamical eigenmodes for the two-dimensional Ising model at the critical temperature with local spin-exchange moves, i.e., Kawasaki dynamics. We obtain the dynamical scaling properties for these modes and use them to calculate the time evolution of two dynamical quantities for the system, namely, the autocorrelation function and the mean-square deviation of the line magnetizations. At intermediate times 1≲t≲Lzc, where zc=4−η=15/4 is the dynamical critical exponent of the model, we find that the line magnetization undergoes anomalous diffusion. Following our recent work on anomalous diffusion in spin models, we demonstrate that the generalized Langevin equation with a memory kernel consistently describes the anomalous diffusion, verifying the corresponding fluctuation-dissipation theorem with the calculation of the force autocorrelation function.

关键词： Anomalous diffusion Magnetization dynamics Phase transitions Equilibrium lattice models Lattice models in statistical physics Stochastic dynamical systems Finite-size scaling Ising model metropolis algorithm Monte Carlo methods

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Melting in two-dimensional systems: Characterizing continuous and first-order transitions

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Physical Review B 2021年第9期103卷 094107-094107页

作者： Óscar Toledano M. Pancorbo J. E. Alvarellos Óscar Gálvez Departamento Física Interdisciplinar Facultad de Ciencias Universidad Nacional de Educación a Distancia (UNED) Senda del Rey 9 28040 Madrid Spain Departamento Física Fundamental Facultad de Ciencias Universidad Nacional de Educación a Distancia (UNED) Senda del Rey 9 28040 Madrid Spain

The mechanisms underlying the melting process in bidimensional systems have been widely studied by means of experiments, theory, and simulations since Kosterlitz, Thouless, Halperin, Nelson, and Young elaborated the KTHNY theory. In the framework of this theory, melting is produced by two continuous transitions mediated by the unbinding of local defects and the appearance of an intermediate phase between solid and liquid, called “hexatic.” There are also other competing theories that could explain this process, as, e.g., the formation of grain boundaries (lines of defects), which lead to a first-order transition. In this paper, simulations of systems interacting via the Lennard Jones 6–12 and Morse potentials using the metropolis Monte Carlo method in the NVT ensemble have been performed to study the effect of the potential shape in the melting process. Additionally, truncated Morse potentials (with only a repulsive part) have been used to investigate the effect of the long-range interactions. Transitions from solid to hexatic phases were found to be continuous for all potentials studied, but transitions from hexatic to liquid phases were found to be either continuous or first order, depending on the thermodynamic conditions and the potential interaction selected, suggesting that melting can be triggered by different mechanisms, like grain boundary formation or defect unbinding. We find that the ratio of defects at the liquid-hexatic or liquid-coexistence phase transitions could determine the nature of these transitions and the mechanism underlying the melting process. The effect of the interaction of particles with their first- and second-nearest neighbors is also discussed.

关键词： Dynamical phase transitions First order phase transitions Geometric & topological phases Second order phase transitions Topological phase transition 2-dimensional systems Ultrathin films metropolis algorithm

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Three-dimensional electroelastic modeling of the nucleation and propagation of the spin domains in spin-crossover materials

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Physical Review B 2022年第1期106卷 014422-014422页

作者： Nicolas di Scala Nour El Islam Belmouri Miguel Angel Paez Espejo Kamel Boukheddaden Université Paris-Saclay Université de Versailles-Saint-Quentin-en-Yvelines Groupe d'Études de la Matière Condensée Unité Mixte de Recherche No 8635 45 Avenue des États Unis Versailles 78035 France

A three-dimensional version of the electroelastic model allowing the description of spin-crossover (SCO) materials taking into account for the volume change at the transition between the LS and the HS spin states is developed. The investigations are realized on a rectangular parallelepiped lattice with cubic symmetry. The SCO units are modeled by two-states fictitious spins coupled by springs whose equilibrium distances depend on the spin states. We implemented massive parallel simulations using CUDA (Compute Unified Device Architecture) programming where the spin states are updated using the Monte Carlo metropolis algorithm, while the mechanical relaxation (lattice position) is performed by molecular dynamics. In this work, we investigated (i) the case of the thermal spin transition showing the macroscopic deformation of the parallelepiped accompanying the propagation of single domains and (ii) the isothermal relaxation of the photoinduced metastable HS fraction at low temperature. In both cases, the interplay between the electronic and the structural aspects of these transformations is analyzed and discussed in relation with the model parameters.

关键词： Elasticity Phase transitions Spin state transition Stress propagation Molecular solids Ising model metropolis algorithm Molecular dynamics Monte Carlo methods Spin lattice models

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Anisotropic exchange Hamiltonian, magnetic phase diagram, and domain inversion of Nd2Zr2O7

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Physical Review B 2019年第14期99卷 144420-144420页

作者： J. Xu Owen Benton V. K. Anand A. T. M. N. Islam T. Guidi G. Ehlers E. Feng Y. Su A. Sakai P. Gegenwart B. Lake Helmholtz-Zentrum Berlin für Materialien und Energie GmbH Hahn-Meitner-Platz 1 D-14109 Berlin Germany Institut für Festkörperphysik Technische Universität Berlin Hardenbergstraße 36 D-10623 Berlin Germany RIKEN Center for Emergent Matter Science (CEMS) Wako Saitama 351-0198 Japan ISIS facility Rutherford Appleton Laboratory Didcot OX11 0QX United Kingdom Oak Ridge National Laboratory Oak Ridge P.O. Box 2008 Tennessee 37831 USA Jülich Centre for Neutron Science JCNS Forschungszentrum Jülich Outstation at MLZ Lichtenbergstr. 1 D-85747 Garching Germany Center for Electronic Correlations and Magnetism Institute of Physics University of Augsburg D-86135 Augsburg Germany

We present thermodynamic and neutron-scattering measurements on the quantum spin ice candidate Nd2Zr2O7. The parametrization of the anisotropic exchange Hamiltonian is refined based on high-energy-resolution inelastic neutron-scattering data together with thermodynamic data using linear spin-wave theory and numerical linked-cluster expansion. Magnetic phase diagrams are calculated using classical Monte Carlo simulations with fields along [100], [110], and [111] crystallographic directions which agree qualitatively with the experiment. Large hysteresis and irreversibility for [111] is reproduced and the microscopic mechanism is revealed by mean-field calculations to be the existence of metastable states and domain inversion. Our results shed light on the explanations of the recently observed dynamical kagome ice in Nd2Zr2O7 in [111] fields.

关键词： Frustrated magnetism Magnetic interactions Spin ice Inorganic compounds Single crystal materials Cluster methods Crystal growth Holstein-Primakoff method Magnetization measurements metropolis algorithm Specific heat measurements Time-of-flight neutron spectroscopy X-ray powder diffraction

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Fluctuations of conformational mobility of macromolecules around the glass transition

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Physical Review E 2018年第6期97卷 062605-062605页

作者： C. Torregrosa Cabanilles J. Molina-Mateo R. Sabater i Serra J. M. Meseguer-Dueñas J. L. Gómez Ribelles Center for Biomaterials and Tissue Engineering Universitat Politècnica de València València Spain

The heterogeneity of local dynamics in disordered systems is behind some key features of glass transition. In order to improve our understanding of the molecular dynamics in disordered systems in the vicinity of the glass transition, different parameters have been proposed to quantitatively describe dynamical heterogeneity. In the case of polymers, free volume models relate the macromolecular mobility to the free or accessible volume. The relationship between dynamic heterogeneity and fluctuations of accessible volume seems straightforward. In the present work, the heterogeneity of local dynamics in polymeric systems is analyzed by computer simulation with the bond fluctuation model. The value of the accessible volume around each polymer chain is evaluated from a snapshot or static structure at each system state, resulting in a distribution of accessible volume that reflects system heterogeneity. The relationship between the average value and the standard deviation of free volume distributions at different temperatures fits a master curve for different systems, regardless of the specific inter- and intramolecular interaction potentials that define each material. The dynamic slowdown around the glass transition is accompanied by a clear evolution of the mean value and shape of the accessible free volume distribution. The relative fluctuation of the dynamically accessible volume has been used as a parameter to quantitatively describe heterogeneity. The fluctuation varies with temperature with remarkable differences between the liquid and glassy states of the systems studied, presenting a peak at the glass transition temperature, which can be interpreted as a reflection of the distribution of local glass transition temperatures.

关键词： Glass transition Polymer behavior Glassy systems Macromolecules Coarse graining metropolis algorithm

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