Ferromagnetic to Paramagnetic Transition in Spherical Spin Glass

Journal of Statistical Physics - We consider the spherical spin glass model defined by a combination of the pure 2-spin spherical Sherrington–Kirkpatrick Hamiltonian and the ferromagnetic...     

Magnetic Transformations and Polymorphic Transition of Ferromagnetic Steels under Shock-Wave Loading

Technical Physics - A method for recording magnetic transformation is presented for ferromagnetic steels under shock-wave loading. The operation of the magnetic transformation gauge is considered...     

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...     

On the Localization Transition of Random Copolymers Near Selective Interfaces

In this note we consider the (de)localization transition for random directed (1+1)–dimensional copolymers in the proximity of an interface separating selective solvents. We derive a rigorous lower bound on the free energy. This yields a substantial improvement on the bounds from below on the critical line that were known so far. Our result implies that the critical curve does not lie below the critical curve set forth by Monthus (Eur. Phys. J. B 13, 111–130, 2000) on the base of a renormalization group analysis. We discuss this result in the light of the (rigorous and non rigorous) approaches present in the literature and, by making an analogy with a particular asymptotics of a disordered wetting model, we propose a simplified framework in which the question of identifying the critical curve, as well as understanding the nature of the transition, may be approached.     

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.     

Stripes and superconductivity in cuprates

Holes doped into the CuO₂ planes of cuprate parent compounds frustrate the antiferromagnetic order. The development of spin and charge stripes provides a compromise between the competing magnetic and kinetic energies. Static stripe order has been observed only in certain particular compounds, but there are signatures which suggest that dynamic stripe correlations are common in the cuprates. Though stripe order is bad for superconducting phase coherence, stripes are compatible with strong pairing. Ironically, magnetic-field-induced stripe order appears to enhance the stability of superconducting order within the planes.     

On the Transition Probability for the Near or Exact Resonance with the RWA

Rotating wave approximation (RWA) has been used to evaluate the transition probability and solve the Schrödinger equation approximately in quantum optics. Examples include the invalidity of the traditional adiabatic condition for the adiabaticity invoking a two-level coupled system near resonance. Here, using a two-state system driven by an oscillatory force, we derive the exact transition probability by solving the Schrödinger equation analytically for a general wave function. Our results reveal that the application of the RWA may lead to false conclusions on the transition probability for the near resonance with weak coupling, especially when the coupling strength is about a half of the transition frequency. We also investigate conditions for which RWA may work or fail.     

干涉条纹的数据拟合方法

如何对干涉条纹数据进行有效地拟合,直接关系到条纹的定位精度以及待测量的检测精度。分析了上前使用的多项式最小二乘拟合法的局限法,提出了一种基于条纹特征的分步拟合新方法。该法避免了非线性拟合问题,其仿真拟合度优于９９．９９％,实验拟合度优于９７．２４％,可有产地对干涉条纹进行实时拟合,并可满意地得到整个序列的拟合曲线。     

Defect Formation in a Dynamic Transition

When a system that undergoes a continuous phase transition is swept through its critical point the initial symmetry is broken and domains are formed. Because of critical slowing down it is not possible to sweep adiabatically; the number of domains therefore depends on the rate of increase of the critical parameter. We give a summary of recent theoretical results for the number of defects produced as a function of how rapidly the transition point is passed. They are obtained from a simplified model, using a stochastic partial differential equation that is also solved numerically.     

Propagation of a Surface Magnetoelastic Wave in a Ferromagnet Near the Orientation Phase Transition

Physics of the Solid State - The frequency dependences of the group velocity and the damping of a magnetoelastic surface wave have been studied at various values of an external magnetic field and...     

Stripes, electron fractionalization, and ARPES

Although structurally the high temperature superconductors are quasi-two-dimensional, there is both theoretical and experimental evidence of a substantial range of temperatures in which ‘stripe’ correlations make the electronic structure locally quasi-one-dimensional. We consider an array of Josephson coupled, spin gapped one dimensional electron gases as a model of the high temperature superconductors. For temperatures above T_c, this system exhibits electron fractionalization, yielding a single particle spectral response which is sharp as a function of momentum, but broad as a function of energy. For temperatures below the spin gap but above T_c, there are enhanced one-dimensional superconducting fluctuations and pseudogap phenomena. Pair tunneling induces a crossover to three-dimensional physics as T_c is approached. Below T_c, solitons are confined in multiplets with quantum numbers which are simply related to the electron, and a coherent piece of the single particle spectral function appears. The weight of this coherent piece vanishes in the neighborhood of T_c in proportion to a positive power of the interchain superfluid density. This behavior is highly reminiscent of recent ARPES measurements on the high temperature superconductors.     

Formation of Annihilation-Cyclotron Lines in Strong Magnetic Fields Near Neutron Stars

We study cyclotron and polarization spectral features in magnetized vacuum at frequencies near the one-photon annihilation resonance in a subcritical magnetic field. On the basis of this study, we propose a new method for determination of the neutron-star magnetic field. Using the dipole-field model, we show that detection of the annihilation line in absorption and an additional line in emission at MeV energies is evidence of the existence of a magnetic field (2.8-3.6)· 10¹²G on the surface of a neutron star.     

Asymptotic Behavior Near Transition Fronts for Equations of Generalized Cahn–Hilliard Form

We consider the asymptotic behavior of perturbations of standing wave solutions arising in evolutionary PDE of generalized Cahn–Hilliard form in one space dimension. Such equations are well known to arise in the study of spinodal decomposition, a phenomenon in which the rapid cooling of a homogeneously mixed binary alloy causes separation to occur, resolving the mixture into its two components with their concentrations separated by sharp transition layers. Motivated by work of Bricmont, Kupiainen, and Taskinen [5], we regard the study of standing waves as an interesting step toward understanding the dynamics of these transitions. A critical feature of the Cahn–Hilliard equation is that the linear operator that arises upon linearization of the equation about a standing wave solution has essential spectrum extending onto the imaginary axis, a feature that is known to complicate the step from spectral to nonlinear stability. Under the assumption of spectral stability, described in terms of an appropriate Evans function, we develop detailed asymptotics for perturbations from standing wave solutions, establishing phase-asymptotic orbital stability for initial perturbations decaying with appropriate algebraic rate.     

Stripes and superconductivity in a one-dimensional self-consistent model

We show that many observable properties of high-temperature superconductors can be obtained in the framework of a one-dimensional self-consistent model with included superconducting correlations. Analytical solutions for spin, charge, and superconductivity order parameters are found. The ground state of the model at low hole doping is a spin-charge solitonic superstructure. Increased doping leads to a transition to the superconducting phase. There is a region of doping where superconductivity, spin density wave, and charged stripe structure coexist. The charge density modulation appears in the vicinity of vortices (kinks in the 1D model) in the superconducting state.     

The Properties of Voronoi Tessellations for 2D Ising Fluid Near the Second-Order Magnetic Phase Transition

The topological and geometrical properties of Voronoi cells generated for 2D fluid of hard disks with Ising-like spins near the second-order phase transition from the paramagnetic to ferromagnetic phase are described for different disk densities. The comparison with Voronoi cells generated for the random hard disk system is given.