Reconstruction on Trees and Spin Glass Transition

Consider an information source generating a symbol at the root of a tree network whose links correspond to noisy communication channels, and broadcasting it through the network. We study the problem of reconstructing the transmitted symbol from the information received at the leaves. In the large system limit, reconstruction is possible when the channel noise is smaller than a threshold.We show that this threshold coincides with the dynamical (replica symmetry breaking) glass transition for an associated statistical physics problem. Motivated by this correspondence, we derive a variational principle which implies new rigorous bounds on the reconstruction threshold. Finally, we apply a standard numerical procedure used in statistical physics, to predict the reconstruction thresholds in various channels. In particular, we prove a bound on the reconstruction problem for the antiferromagnetic “Potts” channels, which implies, in the noiseless limit, new results on random proper colorings of infinite regular trees.This relation to the reconstruction problem also offers interesting perspective for putting on a clean mathematical basis the theory of glasses on random graphs. PACS: 02.50.−r (Probability theory, stochastic processes, and statistics), 64.70.Pf (Glass transitions), 89.75.Hc (Networks and genealogical trees)     

Electron Spin Resonance under Conditions of a Ferromagnetic Phase Transition

JETP Letters - The spin resonance of two-dimensional conduction electrons in a ZnO/MgZnO heterojunction in tilted magnetic fields is studied near the filling factor $$\nu = 2$$ . The analysis of...     

The Percolation Signature of the Spin Glass Transition

Magnetic ordering at low temperature for Ising ferromagnets manifests itself within the associated Fortuin–Kasteleyn (FK) random cluster representation as the occurrence of a single positive density percolating network. In this paper we investigate the percolation signature for Ising spin glass ordering—both in short-range (EA) and infinite-range (SK) models—within a two-replica FK representation and also within the different Chayes–Machta–Redner two-replica graphical representation. Based on numerical studies of the ±J EA model in three dimensions and on rigorous results for the SK model, we conclude that the spin glass transition corresponds to the appearance of two percolating clusters of unequal densities.     

Quantum Phase Transition and Ferromagnetic Spin Correlation in Parallel Double Quantum Dots

We investigate electronic transport through a parallel double quantum dot （DQD） system with strong on-site Coulomb interaction, as well as the interdot tunnelling. By applying numerical renormalization group method, the ground state of the system and the transmission probability at zero temperature are obtained. For a system of quantum dots with degenerate energy levels and small interdot tunnel coupling, the spin correlations between the DQDs is ferromagnetic, and the ground state of the system is a spin-1 triplet state. The linear conductance will reach the unitary limit （2e^2/h） due to the Kondo effect at low temperature. As the interdot tunnel coupling increases, there is a quantum phase transition from ferromagnetic to anti-ferromagnetic spin correlation in DQDs and the linear conductance is strongly suppressed.     

Study of the Two-Dimensional Anisotropic Ising Model with Competing Interactions in the Region of a Transition from the Ferromagnetic to Paramagnetic State

Journal of Experimental and Theoretical Physics - The two-dimensional anisotropic Ising model with competing interactions in the region of a transition from the ferromagnetic to paramagnetic phase...     

Strong-Superstrong Transition in Glass Transition of Metallic Glass

Dynamic fragility of bulk metallic glass （BMG） of Zr64Cu16Ni10Al10 alloy is studied by three-point beam bending methods. The fragility parameter mfor Zr64Cu16Ni10Al10 BMG is calculated to be 24.5 at high temperature, which means that the liquid is a ＂strong＂ liquid, while to be 13.4 at low temperature which means that the liquid is a ＂super-strong＂ liquid. The dynamical behavior of Zr64Cu16Ni10Al10 BMG in the supercooled region undergoes a strong to super-strong transition. To our knowledge, it is the first time that a strong-to-superstrong transition is found in the metallic glass. Using small angle x-ray scattering experiments, we find that this transition is assumed to be related to a phase separation process in supercooled liquid.     

Features of EPR Application to Systems Containing Paramagnetic Centers and Ferromagnetic Nanoparticles

The scope of the electron paramagnetic resonance (EPR) technique in catalysis is often limited because of the presence of the ferromagnetic nanoparticles in many catalytic systems. The present work gives an effective method to discriminate solid-state EPR spectra in the microwave resonance absorption while investigating such systems. The approach is based on the different features of the EPR spectra and ferromagnetic resonance absorption that are simultaneously observed in the system.     

Spin Exchange Between Charged Paramagnetic Particles in Dilute Solutions

Kinetic equations for the spin density matrix which take into account binary collisions and a method of calculating the spin exchange effective radius have been generalized to the case of dilute solutions of charged paramagnetic particles. The effective radius of the spin exchange and rate constant of the bimolecular spin exchange between charged paramagnetic particles in solutions have been calculated numerically. Calculations have been performed under the assumption that the exchange interaction is isotropic and decays exponentially with the increase in the distance between radicals, and the solution has a given dielectric permittivity and Debye screening radius. Dependences of the spin exchange rate constant on the mutual diffusion coefficient, exchange and electrostatic interactions parameters have been found numerically. The theory has been applied to experimental results taken from the literature. The rate constant of the spin exchange between radicals of like charge found from the experiment and calculated within the developed theory are in good qualitative agreement .     

Transport Through a Precessing Spin Coupled to Noncollinearly Polarized Ferromagnetic Leads

The quantum electronic transport through a precessing magnetic spin coupled to noncollinearly polarized ferromagnetic leads （F-MS-F） has been studied in this paper. The nonequilibrium Green function approach is used to calculate local density of states （LDOS） and current in the presence of external bias. The characters of LDOS and the electronic current are obtained. The tunneling current is investigated for different precessing angle and different configurations of the magnetization of the leads. The investigation revea/s that when the precessing angle takes θ 〈 π /2 and negative bias is applied, the resonant tunneling current appears, otherwise, it appears when positive bias is applied. When the leads are totally polarized and the precessing angel takes O, the tunneling current changes with the configuration of two leads; and it becomes zero when the two leads are antiparallel.     

Some Spin Glass Ideas Applied to the Clique Problem

In this paper we introduce a new algorithm to study some NP-complete problems. This algorithm is a Markov Chain Monte Carlo (MCMC) inspired by the cavity method developed in the study of spin glass. We will focus on the maximum clique problem and we will compare this new algorithm with several standard algorithms on some DIMACS benchmark graphs and on random graphs. The performances of the new algorithm are quite surprising. Our effort in this paper is to be clear as well to those readers who are not in the field.     

高性能大口径顺磁旋光玻璃

旋光玻璃广泛用于激光的调制、偏转、开关和高功率激光系统的隔离器.旋光玻璃的主要性质为费尔德常数.含高顺磁离子的旋光玻璃具有大的费尔德常数,可见区高透过等优点.具有较大磁矩和较低f-d跃迁能隙的顺磁离子铽应具有大的费尔德常数.本工作以高Tb2O3含量的Tb2 O3-B2O3-Al2O3-SiO2为基本系统.研究玻璃的形成;测定了不同Tb3+离子浓度时的费尔德常数,符合线性关系;调整玻璃组成以避免析晶,发展了波长632 nm的费尔德常数为75.1～116.4 rad/(T·m)的TG20,TG28,TG32旋光玻璃系列.建立了10升规模铂坩埚高温熔炉,成形和退火设备.形成口径30 cm旋光玻璃的生产能力.产品的1054 nm光吸收小于0.008 cm-1,1 ns的激光破坏阈值大于8 J/cm2,透过波前畸变小于五分之一波长.所制造的旋光玻璃已用于美国Lawrence Livermore国家实验室,中国"神光Ⅱ"升级,英国Rutherford实验室的Vulcan Laser System和CNRS CEA Luli等高功率激光系统.     

Spin Wave Spectra of Ferromagnetic Superlattice with Antiparallel Magnetization

In this paper, by using the Holstein-Primakoff (HP) and Bogoliu bov transformation, the spin wave spectra of ferromagnetic/nonmagnetic superlattice with antiparallel magnetizations between the neighboring ferromagnetic films are studied. The effects of some magnetic parameters on the spin wave spectra are discussed in detail.     

Magnetoelectric Coupling Induced Electric Dipole Glass State in Heisenberg Spin Glass

Multiferroic behavior in an isotropic Heisenberg spin glass with Gaussian random fields, incorporated by magneto-electric coupling derived from the Landau symmetry argument, are investigated. Electric dipole glass transitions at finite temperature, due to coupling, are demonstrated by Monte Carlo simulation. This electric dipole glass state is solely ascribed to the coupling term with chiral symmetry of the magnetization, while the term associated with the spatial derivative of the squared magnetization has no contribution.     

Ferrimagnetic to Paramagnetic Transition in Magnetite: Mössbauer versus Monte Carlo

Powder magnetite was analyzed in situ via Mössbauer with temperatures ranging from 170 K up to 900 K. Hyperfine fields of the tetrahedral and octahedral sites of magnetite as well as the corresponding average field were followed as a function of temperature in order to elucidate the critical behavior of magnetite at around the Curie temperature. Results evidence a progressive collapse of the Mössbauer spectra onto a singlet-type line at a critical temperature of around 870 K characterized by a critical exponent β = 0.28(2) for the hyperfine field. In order to describe such temperature dependence of the hyperfine field, a Monte Carlo-Metropolis simulation based on a stoichiometric magnetite and an Ising model with nearest magnetic neighbor interactions was also carried out. In the model, we have taken into account antiferromagnetic and ferromagnetic interactions depending on the involved ions. A discussion about the critical behavior of magnetite and a comparison between the hyperfine field obtained via Mössbauer and the magnetization obtained via Monte Carlo is finally presented.     

Mode Structures and Damping of Quantized Spin Waves in Ferromagnetic Nanowires

Magnonic devices based on spin waves are considered as a new generation of energy-efficient and high-speed devices for storage and processing of information. Here we experimentally demonstrate that three distinct dominated magneto-dynamic modes are excited simultaneously and coexist in a transversely magnetized ferromagnetic wire by the ferromagnetic resonance(FMR) technique. Besides the uniform FMR mode, the spin-wave well mode, the backward volume magnetostatic spin-wave mode, and the perpendi...     

Swap of Information between Two-End States in an Open Ferromagnetic Spin Chaint

The bidirectional transfer of information can be realized in an open Heisenberg ferromagnetic spin chain. The information is encoded in the probability distributions of the states at two end spins. The relative entropy is used to evaluate the effective transmission of the probability. The evolution of the relative entropy shows a periodical behavior. The period is increased with increasing the length of the chain and the magnetic field while it decreases with increasing the coupling strength.