Breakdown of scaling in the nonequilibrium critical dynamics of the two-dimensional XY model

The approach to equilibrium, from a nonequilibrium initial state, in a system at its critical point is usually described by a scaling theory with a single growing length scale, xi(t) approximately t(1/z), where z is the dynamic exponent that governs the equilibrium dynamics. We show that, for the 2D XY model, the rate of approach to equilibrium depends on the initial condition. In particular, xi(t) approximately t(1/2) if no free vortices are present in the initial state, while xi(t) approximately (t/lnt)(1/2) if free vortices are present.     

Dipole orientational order at liquid/vapor surfaces

We present ellipsometric observations of the orientational order alpha(2) of highly polar molecules at the noncritical liquid/vapor surface of critical polar+nonpolar mixtures. The dipoles, which are repelled from the interface via interactions with their image dipoles, are preferentially oriented with their axes parallel to the surface and possess an orientational order which is well described by alpha(2) approximately -t(2beta)D+(z/xi), where t=[T-T(c)]/T(c) is the reduced temperature, beta=0.328 is a critical exponent, and D+ is a universal function of the dimensionless depth z/xi with surface correlation length xi.     

Kinetic roughening of ion-sputtered Pd(001) surface: beyond the Kuramoto-Sivashinsky model

We investigate the kinetic roughening of Ar+ ion-sputtered Pd(001) surface both experimentally and theoretically. In situ real-time x-ray reflectivity and in situ scanning tunneling microscopy show that nanoscale adatom islands form and grow with increasing sputter time t. Surface roughness W(t) and lateral correlation length xi(t) follow the scaling laws W(t) approximately t(beta) and xi(t) approximately t(1/z) with the exponents beta approximately 0.20 and 1/z approximately 0.20, for an ion beam energy epsilon=0.5 keV, which is inconsistent with the prediction of the Kuramoto-Sivashinsky (KS) model. We thereby extend the KS model by applying the coarse-grained continuum approach of the Sigmund theory to the order of O(inverted Delta(4),h(2)), where h is the surface height, and derive a new term of the form inverted Delta(2)(inverted Delta h)(2) which plays a decisive role in describing the observed morphological evolution of the sputtered surface.     

Kinetic roughening in polymer film growth by vapor deposition

The growth front roughness of linear poly( p-xylylene) films grown by vapor deposition polymerization has been investigated using atomic force microscopy. The interface width w increases as a power law of film thickness d, w approximately d(beta), with beta = 0. 25+/-0.03, and the lateral correlation length xi grows as xi approximately d(1/z), with 1/z = 0.31+/-0.02. This novel scaling behavior is interpreted as the result of monomer bulk diffusion, and belongs to a new universality class that has not been discussed previously.     

Anisotropies of the lower and upper critical fields in MgB2 single crystals

The temperature dependence of the upper (H(c2)) and lower (H(c1)) critical fields has been deduced from Hall probe magnetization measurements of high quality MgB2 single crystals along the two main crystallographic directions. We show that Gamma(H(c2))=H(c2 axially ab)/H(c2 axially c) and Gamma(H(c1))=H(c1 axially c)/H(c1 axially ab) differ significantly at low temperature (being approximately 5 and approximately 1, respectively) and have opposite temperature dependencies. We suggest that MgB2 can be described by a single field dependent anisotropy parameter gamma(H) (=lambda(c)/lambda(ab)=xi(ab)/xi(c)) that increases from Gamma(H(c1)) at low field to Gamma(H(c2)) at high field.     

Anomalous dielectric behavior of water in ionic newton black films

The electrostatics of two charged surfactant layers in aqueous media (surfactant/water/surfactant films) is investigated using molecular dynamics simulations. In the films studied (with a surfactant-surfactant distance from approximately 35 A to contact) we observe an anomalous dielectric response of water. The electrostatic potential phi(z) inside the aqueous core of the films (containing bulk water with rho=1 g/cm(3)) is completely different from that expected for a film containing a dielectric medium with the dielectric constant of water. In addition, our results are not consistent with a local relation between the water polarization P(z)(z) and the electric field E(z)(z). The polarization P(z)(z) is maximum at the interfaces (due to solvent molecules forming part of the structure of the surfactant layers) and decays from the interfaces inside the aqueous core with a decay length of order of approximately 10 A.     

Crossover between ordinary and normal transitions in two dimensional critical Ising films

We investigate two dimensional critical Ising films of width L with surface fields H(1)=H(L) in the crossover between ordinary (H(1)=0) and normal (H(1)=infinity) transitions. Using exact transfer-matrix diagonalization and density matrix renormalization-group (DMRG) methods, we calculate magnetization profiles m(z), the excess magnetization Gamma, and the analog of the solvation force f(solv) as functions of H1 for several L. Scaling functions of the above quantities deviate substantially from their asymptotic forms at fixed points for a broad region of the scaling variable LH21 approximately L/l(1), where l(1) is the length induced by the surface field H1. The scaling function for /f(solv)/ has a deep minimum near LH(2)(1)=1, which is about one order of magnitude smaller than its value at both fixed points (the "Casimir" amplitude). For weak H1 (l(1)>L) the magnetization profile has a maximum at the center of the film, and f(solv) decays much faster than L-2. For stronger H1 (1l(1) the solvation force decays according to the universal power law f(solv) approximately L(-2). The results of the approximate DMRG method show remarkable agreement with the exact ones.     

Inertial mass of the Abrikosov vortex

We show that a large contribution to the inertial mass of the Abrikosov vortex comes from transversal displacements of the crystal lattice. The corresponding part of the mass per unit length of the vortex line is M(l)=(m(2)(e)c(2)/64 pi alpha(2)mu lambda(4)(L))ln((lambda(L)/xi), where m(e) is the bare electron mass, c is the speed of light, alpha=e(2)/Planck's over 2 pi c approximately 1/137 is the fine structure constant, mu is the shear modulus of the solid, lambda(L) is the London penetration length, and xi is the coherence length. In conventional superconductors, this mass can be comparable to or even greater than the vortex core mass computed by Suhl [Phys. Rev. Lett. 14, 226 (1965)]].     

Passive scalar intermittency in low temperature helium flows

We report new measurements of mixing of passive temperature field in a turbulent flow. The use of low temperature helium gas allows us to span a range of microscale Reynolds number, R(lambda), from 100 to 650. The exponents xi(n) of the temperature structure functions approximately r(xi(n)) are shown to saturate to xi(infinity) approximately 1.45+/-0.1 for the highest orders, n approximately 10. This saturation is a signature of statistics dominated by frontlike structures, the cliffs. Statistics of the cliffs' characteristics are performed, particularly their widths are shown to scale as the Kolmogorov length scale.     

Quantum gravity corrections to neutrino propagation

Massive spin-1/2 fields are studied in the framework of loop quantum gravity by considering a state approximating, at a length scale L much greater than Planck length l(P), a spin-1/2 field in flat spacetime. The discrete structure of spacetime at l(P) yields corrections to the field propagation at scale L. Neutrino bursts ( &pmacr; approximately 10(5) GeV) accompanying gamma ray bursts that have traveled cosmological distances L are considered. The dominant correction is helicity independent and leads to a time delay of order (&pmacr;l(P))L/c approximately 10(4) s. To next order in &pmacr;l(P), the correction has the form of the Gambini and Pullin effect for photons. A dependence L(-1)(os) approximately &pmacr;(2)l(P) is found for a two-flavor neutrino oscillation length.     

Critical fluctuations and quenched disordered two-dimensional charge stripes in La(5/3)Sr(1/3)NiO4

Using high-resolution x-ray scattering, we have demonstrated the existence of quenched disordered charge stripes in a single crystal of La (5/3)Sr (1/3)NiO (4) at low temperatures. Above the second-order transition critical scattering was observed due to fluctuations into the charge stripe phase. The charge stripes are shown to be two dimensional in nature both by measurements of their correlation lengths (xi(a) approximately 185 A, xi(b) = 400 A, and xi(c) approximately 25 A) and by the critical exponents of the charge strip transition. The charge stripe ordering did not develop long-range order even at low temperatures, indicating that the charge stripes are disordered and that the length scale of the disorder is quenched.     

Exact results for quench dynamics and defect production in a two-dimensional model

We show that for a d-dimensional model in which a quench with a rate tau(-1) takes the system across a (d-m)-dimensional critical surface, the defect density scales as n approximately 1/tau(mnu/(znu+1)), where nu and z are the correlation length and dynamical critical exponents characterizing the critical surface. We explicitly demonstrate that the Kitaev model provides an example of such a scaling with d = 2 and m = nu = z = 1. We also provide the first example of an exact calculation of some multispin correlation functions for a two-dimensional model that can be used to determine the correlation between the defects. We suggest possible experiments to test our theory.     

Breakdown of dynamic scaling in surface growth under shadowing

Using Monte Carlo simulations and experimental results, we show that for common thin film deposition techniques, such as sputter deposition and chemical vapor deposition, a mound structure can be formed with a characteristic length scale, or "wavelength" lambda, that describes the separation of the mounds. We show that the temporal evolution of lambda is distinctly different from that of the mound size, or lateral correlation length xi. The formation of a mound structure is due to nonlocal growth effects, such as shadowing, that lead to the breakdown of the self-affinity of the morphology described by the well-established dynamic scaling theory. We show that the wavelength grows as a function of time in a power law form, lambda approximately t(p), where p approximately equals 0.5 for a wide range of growth conditions, while the mound size grows as xi approximately t(1-z), where 1/z varies depending on growth conditions.     

Coherent "metallic" resistance and medium localization in a disordered one-dimensional insulator

It is believed that a disordered one-dimensional (1D) wire with coherent electronic conduction is an insulator with the mean resistance approximately equal e(2L/xi) and resistance dispersion Delta(rho) approximately equal e(L/xi), where L is the wire length and xi is the electron localization length. Here we show that this 1D insulator undergoes at full coherence the crossover to a 1D "metal," caused by thermal smearing and resonant tunneling. As a result, Delta(rho) is smaller than unity and tends to be L/xi independent, while grows with L/xi first nearly linearly and then polynomially, manifesting the so-called medium localization.     

Critical properties of lattices of diffusively coupled quadratic maps

We study the critical properties of lattices of coupled logistic maps in the regime where the individual maps are closely above the onset of chaos. We discuss both spatial and temporal characteristics and especially the link between them. We show that the mutual information function between two points on the lattice decays exponentially with distance. In this way we find support for the relation xi approximately lambda(-1/2) between the coherence length xi and the largest Lyapunov exponent lambda which is further corroborated by a detailed study of the spreading of small perturbations. Finally we study the structure function of the lattice field variable. It shows that at the onset of chaos the lattice remains smooth.     

Molecular dynamics simulations of a fluid near its critical point

We present computer simulations for the static and dynamic behavior of a fluid near its consolute critical point. We study the Widom-Rowlinson mixture, which is a two component fluid where like species do not interact and unlike species interact via a hard core repulsion. At high enough densities this fluid exhibits a second order demixing transition that is in the Ising universality class. We find that the mutual diffusion coefficient DAB vanishes as DAB approximately xi(-1.26 +/- 0.08), where xi is the correlation length. This is different from renormalization-group and mode coupling theory predictions for model H, which are DAB approximately xi(-1.065) and DAB approximately xi(-1), respectively.     

Proof of breaking of self-organized criticality in a nonconservative abelian sandpile model

By computer simulations, it was reported that the Bak-Tang-Wiesenfeld (BTW) model loses self-organized criticality (SOC) when some particles are annihilated in a toppling process in the bulk of system. We give a rigorous proof that the BTW model loses SOC as soon as the annihilation rate becomes positive. To prove this, a nonconservative Abelian sandpile model is defined on a square lattice, which has a parameter alpha (>/=1) representing the degree of breaking of the conservation law. This model is reduced to be the BTW model when alpha=1. By calculating the average number of topplings in an avalanche exactly, it is shown that for any alpha>1, with an exponent 1 as alpha-->1 gives a scaling relation 2nu(2-a)=1 for the critical exponents nu and a of the distribution function of T. The 1-1 height correlation C11(r) is also calculated analytically and we show that C11(r) is bounded by an exponential function when alpha>1, although C11(r) approximately r(-2d) was proved by Majumdar and Dhar for the d-dimensional BTW model. A critical exponent nu(11) characterizing the divergence of the correlation length xi as alpha-->1 is defined as xi approximately |alpha-1|(-nu(11)) and our result gives an upper bound nu(11)相似文献   

Long-range proximity effects in superconductor-ferromagnet structures

We analyze the proximity effect in a superconductor/ferromagnet (S/F) structure with a local inhomogeneity of the magnetization in the ferromagnet near the S/F interface. We demonstrate that not only the singlet but also the triplet component of the superconducting condensate is induced in the ferromagnet due to the proximity effect. The singlet component penetrates into the ferromagnet over a short length xi(h) = sqrt[D/h] ( h is the exchange field and D the diffusion coefficient), whereas the triplet component penetrates over a long length sqrt[D/epsilon] and leads to a significant increase of the ferromagnet conductance below the superconducting critical temperature Tc.     

Evolution of magnetic fields in freely decaying magnetohydrodynamic turbulence

We study the evolution of magnetic fields in freely decaying magnetohydrodynamic turbulence. By quasilinearizing the Navier-Stokes equation, we solve analytically the induction equation in the quasinormal approximation. We find that, if the magnetic field is not helical, the magnetic energy and correlation length evolve in time, respectively, as E(B) proportional to t(-2(1+p)/(3+p)) and xi(B) proportional to t(2/(3+p)), where p is the index of initial power-law spectrum. In the helical case, the magnetic helicity is an almost conserved quantity and forces the magnetic energy and correlation length to scale as E(B) proportional to (logt)(1/3)t(-2/3) and xi(B) proportional to (logt)(-1/3)t(2/3).     

Critical Casimir effect in three-dimensional Ising systems: measurements on binary wetting films

The critical Casimir force (CF) is observed in thin wetting films of a binary liquid mixture close to the liquid/vapor coexistence. X-ray reflectivity shows thickness (L) enhancement near the bulk consolute point. The extracted Casimir amplitude Delta(+-)=3+/-1 agrees with the theoretical universal value for the antisymmetric 3D Ising films. The onset of CF in the one-phase region occurs at L/xi approximately 5 regardless of whether the bulk correlation length xi is varied with temperature or composition. The shape of the Casimir scaling function depends monotonically on the dimensionality.