Cluster structure and the first-order phase transition in dipolar systems

The European Physical Journal E - The Monte Carlo technique is used to simulate a 3D dipolar hard-sphere system. The spatial and magnetic structure of clusters formed by magnetic dipolar...     

Laserlight — first example of a second-order phase transition far away from thermal equilibrium

We solve the functional Fokker-Planck equation established in a previous paper in the vicinity of laser threshold. The stationary solution is obtained explicitly in the formP=N exp [??({ū, ū*})]. ? has exactly the same form as the Ginzburg-Landau expression for the free energy of a superconductor, if the pair wave function is replaced by the electromagnetic field amplitudeū. This gives us the key for a thermodynamic reinterpretation of all laser phenomena. In particular the laser threshold appears as a second-order phase transition in all details. It is indicated that our theory provides a new formalism also for the Ginzburg-Landau theory.     

Correlations in classical and quantum systems far from thermal equilibrium

We consider classical systems described by a Fokker-Planck equation or a generalized Fokker-Planck equation and quantum systems described by a density matrix equation or by a generalized Fokker-Planck equation using the principle of quantum classical correspondence. We split the corresponding operators of the equation of motion into a part which refers to the proper system and another one which describes the coupling of the proper system to the external world (reservoirs). We demonstrate that by use of conservation laws, referring to the proper systems, exact relations hold for certain moments, valid for all temperatures and coupling constants of the reservoirs. Using the concepts of a previous paper we describe then a perturbation theoretical approach which allows in a simple manner to determine a number of important correlation functions (moments of the total system). The time dependent case is briefly discussed. The applicability and usefulness of the present procedure is demonstrated by the example of the single-mode laser yielding e.g. expressions for the atom-field correlation.     

Distribution function for systems far from thermal equilibrium

We present the general stationary solution of the Fokker-Planck equation for a system of interacting subsystems weakly coupled to reservoirs at different temperatures, T_j. For T_j = T, it reduces to the Boltzman distribution function.     

Phase transitions far from thermal equilibrium in spin systems

The nonlinear effects in the spin resonance due to the negative differential r.f. magnetic susceptibility are considered. The r.f. magnetization is shown to exhibite a kind of first order phase transition. A set of scaling relations, valid near the appropriate critical point, is obtained.     

Interrelationship between kinetics and local hydrodynamics for states far from equilibrium

This study examines the kinetic theory of a nonrelativistic gas with internal degrees of freedom in the absence of hydrodynamic sources. The author showed previously for the case of weak sources that the kinetic theory is equivalent to nonlocal hydrodynamics. Here, this result is generalized to the case of sources of arbitrary intensity, when the theory is nonlinear. The nonlocality kernels that appear in the material relations are calculated from the kinetic equation. The methods of perturbation theory are used to find a procedure for successive calculation of the kernels that appear in the higher nonlinear terms. Institute of Earth Physics, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, p. 67–71, August, 1996.     

On time-dependent relaxation-times in semiconductors far from equilibrium

It has long been customary to perform studies of transport properties in matter in terms of a relaxation-time collision operator approximation for the scattering operators in the rate equations. In many-body systems in far-from-equilibrium conditions the application of such a technique is severely limited. This is a consequence of the strong relaxation effects that take place in the sample, which produce large variations in the macroscopic state of the system while it is probed. We discuss here the case of photoexcited polar semiconductors, and we have obtained expressions for the time-dependence of the relevant transport coefficients.     

二维声学系统中的拓扑相变及边界传输

拓扑声学的发现产生了一种可以有效抑制反射的声学边界传输态,不仅让人们重新认识了声传输现象,也扩展了声学新原理功能器件的研究领域。文章将介绍二维系统中拓扑声学的基本概念以及一些拓扑非平庸体系。主要关注利用背景流体构造的声类量子霍尔效应,利用共振耦合环形波导构造Floquet拓扑绝缘体,声类量子自旋霍尔效应以及声谷霍尔效应等。     

A thermodynamic variational principle in nonlinear systems far from equilibrium

The simplest viewpoint of nonlinear systems far from equilibrium suggests that the state of maximum entropy production is most stable among various possible metastable states under external perturbation for immobile boundaries, and that the shape with maximum increasing rate of entropy production is stabilized for mobile boundaries. Examples of computer simulation are demonstrated for a chemical structure and a growing random pattern.     

Recent advances on glass-forming systems driven far from equilibrium

The nature of the glass transition is one of the frontier questions in Statistical Physics and Materials Science. Highly cooperative structural processes develop in glass-forming melts exhibiting relaxational dynamics which is spread out over many decades in time. While considerable progress has been made in recent decades towards understanding dynamical slowing-down in quiescent systems, the interplay of glassy dynamics with external fields reveals a wealth of novel phenomena yet to be explored.This special issue focuses on recent results obtained by the Research Unit FOR 1394 ‘Nonlinear response to probe vitrification’ which was funded by the German Science Foundation (DFG). In the projects of the research unit, strong external fields were used in order to gain insights into the complex structural and transport phenomena at the glass transition under far-from-equilibrium conditions. This aimed inter alia to test theories of the glass transition developed for quiescent systems by pushing them beyond their original regime. Combining experimental, simulational, and theoretical efforts, the eight projects within the FOR 1394 measured and determined aspects of the nonlinear response of supercooled metallic, polymeric, and silica melts, of colloidal dispersions, and of ionic liquids. Applied fields included electric and mechanic fields, and forced active probing (‘micro-rheology’), where a single probe is forced through the glass-forming host. Nonlinear stress-strain and force-velocity relations as well as nonlinear dielectric susceptibilities and conductivities were observed. While the physical manipulation of melts and glasses is interesting in its own right, especially technologically, the investigations performed by the FOR 1394 suggest to use the response to strong homogeneous and inhomogeneous fields as technique to explore on the microscopic level the cooperative mechanisms in dense melts of strongly interacting constituents. Questions considered concern the (de-)coupling of different dynamical degrees of freedom in an external field, and the ensuing state diagrams. What forces are required to detach a localized probe particle from its initial environment in a supercooled liquid, in a glassy or granular system? Do metallic and colloidal glasses yield homogeneously or by strain localization under differently applied stresses? Which mechanisms determine field-dependent susceptibilities in dielectric and ionically conducting glass formers?     

Cluster structure and the first-order phase transition in dipolar systems Monte Carlo simulation

: The Monte Carlo technique is used to simulate a 3D dipolar hard-sphere system. The spatial and magnetic structure of clusters formed by magnetic dipolar interactions in zero applied field is investigated. It is shown that the many-particle clusters are characterized by a quasi-spherical shape, extremely small magnetic moments, and a fractal dimension close to three. These clusters are regarded as nuclei of a new concentrated isotropic phase. The numerical simulation of the first-order phase transition has been realized which allows us to find the interface between two coexisting phases. It has been found that the dipole-dipole and steric interactions are sufficient to separate the system into two phases with low and high concentrations of particles. The introduction of any additional attraction potential is not required. The phase diagram of dipolar system in zero applied field has been obtained. The simulation results are in qualitative agreement with the predictions of some analytical models.     

Field-dependence of the first-order phase transition in terbium phosphide

Magnetization measurements confirm the presence of a strong quadrupolar coupling between the Tb³⁺, responsible for the discontinuous nature of the transition, and show a reduction of T_N proportional to H². This behaviour contrasts with recent renormalization-group predictions for TbP, but can be quantitatively explained within a mean-field model.     

Fermi surface reconstruction in strongly correlated Fermi systems as a first-order phase transition

A quantum phase transition in strongly correlated Fermi systems beyond the topological quantum critical point has been studied using the Fermi liquid approach. The transition takes place between topologically equivalent states with three Fermi surface sheets, but one of them is characterized by a quasiparticle halo in the quasiparticle momentum distribution n(p), and the other one is characterized by a hole pocket. It has been found that the transition between these states is a first-order phase transition for the interaction constant g and temperature T. The phase diagram in the vicinity of this transition has been constructed.     

Gibbs free energy and thermodynamic equilibrium boundary condition for a first-order phase transition in an isotropic solid

Journal of Experimental and Theoretical Physics - For elastic deformation of arbitrary magnitude in an isotropic solid, Legendre conjugate strain variables are found and used to define the Gibbs...     

Gravitational waves from cosmic strings after a first-order phase transition

We study the possibility of probing high scale phase transitions that are inaccessible by LIGO. Our study shows that the stochastic gravitational-wave radiation from cosmic strings that are formed after the first-order phase transition can be detected by space-based interferometers when the phase transition temperature is \begin{document}$ T_n\sim {\cal{O}}(10^{8-11}) $\end{document} GeV.     

Hysteresis and first-order phase transition in the two-dimensional electron gas

We report experimental evidence of the first-order phase transitions in the two-dimensional electron gas formed in a gated wide GaAs/AlGaAs quantum well at even-integer quantum-Hall states. At the filling factor values of ν=2,4 and low temperatures, crossing of Landau levels through the application of the gate bias yields a suppression of the quantum-Hall-state excitation gap and hysteretical behaviour of the diagonal resistivity in up and down sweeps of the magnetic field. Detailed many-body calculations indicate the occurrence of a first-order phase transition and allow the determination of the exact properties of the electron ground states involved in the transition.     

Distribution function for classical and quantum systems far from thermal equilibrium

We consider a system composed of many subsystems which are coupled to individual reservoirs at different temperatures. We show how the solution of a many-dimensional Fokker-Planck equation may be reduced to a Fokker-Planck equation of dimensionn, wheren is the number of relevant constants of motion. We treat also a Fokker-Planck equation with continuously many variables and the time-dependent one. The usefulness of the present procedure to determine explicitly distribution functions is exhibited by several examples. If all temperatures are equal the Boltzman distribution function is obtained as a special case. Using the method of quantum-classical correspondence, the distribution function for quantum systems may be found.