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1.
We investigate the role played by symmetry conserving quenched disorder on quantum criticality of a variety of d-dimensional systems with a continuous symmetry order parameter. We employ a non-standard procedure which combines a preliminary reduction to an effective classical random problem and a successive conventional renormalization group treatment. Solving the effective flow equations to first order in ε=4−d and then restoring the original coupling parameters, for d<4 we find a quantum critical point scenario exhibiting unusual features, which remind us of some predictions of the quantum Griffiths phase model. 相似文献
2.
3.
We present a new general and much simpler scheme to construct various quantum phase transitions (Q, PTs) in spin chain systems with matrix product ground states. By use of the scheme we take into account one kind of matrix product state (MPS) OPT and provide a concrete model. We also study the properties of the concrete example and show that a kind of Q, PT appears, accompanied by the appearance of the discontinuity of the parity absent block physical observable, diverging correlation length only for the parity absent block operator, and other properties which are that the fixed point of the transition point is an isolated intermediate-coupling fixed point of renormalization flow and the entanglement entropy of a half-infinite chain is discontinuous. 相似文献
4.
Hans-Karl Janssen 《Annals of Physics》2005,315(1):147-192
We review the field theory approach to percolation processes. Specifically, we focus on the so-called simple and general epidemic processes that display continuous non-equilibrium active to absorbing state phase transitions whose asymptotic features are governed, respectively, by the directed (DP) and dynamic isotropic percolation (dIP) universality classes. We discuss the construction of a field theory representation for these Markovian stochastic processes based on fundamental phenomenological considerations, as well as from a specific microscopic reaction-diffusion model realization. Subsequently we explain how dynamic renormalization group (RG) methods can be applied to obtain the universal properties near the critical point in an expansion about the upper critical dimensions dc = 4 (DP) and 6 (dIP). We provide a detailed overview of results for critical exponents, scaling functions, crossover phenomena, finite-size scaling, and also briefly comment on the influence of long-range spreading, the presence of a boundary, multispecies generalizations, coupling of the order parameter to other conserved modes, and quenched disorder. 相似文献
5.
In the present work we study the critical properties of the ferromagnetic three-color Ashkin-Teller model (3AT) by means of a Migdal-Kadanoff renormalization group approach on a diamond-like hierarchical lattice. The analysis of the fixed points and flux diagram of the recursion relations is used to determine the corresponding phase diagram (including its symmetry properties) and critical exponents. Our numerical results show the presence of four universality classes, three of them are associated to the Potts model with q=2, 4 and 6 states. Finally, a connection between our findings and some known results from the literature is presented. 相似文献
6.
J.E. Santos U.C. Täuber 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(4):423-440
Second-order phase transitions in a non-equilibrium liquid-gas model with reversible mode couplings, i.e., model H for binary-fluid critical dynamics, are studied using dynamic field theory and the renormalization group. The system
is driven out of equilibrium either by considering different values for the noise strengths in the Langevin equations describing
the evolution of the dynamic variables (effectively placing these at different temperatures), or more generally by allowing
for anisotropic noise strengths, i.e., by constraining the dynamics to be at different temperatures in d
|| - and d
⊥-dimensional subspaces, respectively. In the first, isotropic case, we find one infrared-stable and one unstable renormalization group fixed point. At the stable fixed point, detailed
balance is dynamically restored, with the two noise strengths becoming asymptotically equal. The ensuing critical behavior
is that of the standard equilibrium model H. At the novel unstable fixed point, the temperature ratio for the dynamic variables
is renormalized to infinity, resulting in an effective decoupling between the two modes. We compute the critical exponents
at this new fixed point to one-loop order. For model H with spatially anisotropic noise, we observe a critical softening only in the d
⊥-dimensional sector in wave vector space with lower noise temperature. The ensuing effective two-temperature model H does
not have any stable fixed point in any physical dimension, at least to one-loop order. We obtain formal expressions for the
novel critical exponents in a double expansion about the upper critical dimension d
c = 4 - d
|| and with respect to d
|| , i.e., about the equilibrium theory.
Received 4 April 2002 Published online 13 August 2002 相似文献
7.
J.E.S. Socolar D.G. Schaeffer P. Claudin 《The European physical journal. E, Soft matter》2002,7(4):353-370
A theory of stress fields in two-dimensional granular materials based on directed force chain networks is presented. A general
Boltzmann equation for the densities of force chains in different directions is proposed and a complete solution is obtained
for a special case in which chains lie along a discrete set of directions. The analysis and results demonstrate the necessity
of including nonlinear terms in the Boltzmann equation. A line of nontrivial fixed-point solutions is shown to govern the
properties of large systems. In the vicinity of a generic fixed point, the response to a localized load shows a crossover
from a single, centered peak at intermediate depths to two propagating peaks at large depths that broaden diffusively.
Received 16 January 2002 相似文献
8.
We present the renormalization group (RG) flow diagram of a spin-half antiferromagnetic chain with magnetic impurity and one altered link. In this two parameters (competing interactions) model, one can find the complex phase diagram with many interesting fixed points. There is no evidence of intermediate stable fixed point in weak coupling phase. It may arise at the strong coupling phase. Depending on the strength of couplings the phases correspond either to a decoupled spin with Curie law behavior or a logarithmically diverging impurity susceptibility as in the two channel Kondo problem. 相似文献
9.
S. Müller L. Schäfer 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):351-369
We give a detailed analysis of the intersection properties of polymers. Using the renormalization group we provide a full
crossover function for the dependence of the number of intersections in a single polymer on chain length and excluded volume
strength. We compare our results with Monte-Carlo data and with exact calculations for a random walk, finding good agreement
in all respects. Restricting to the vicinity of the eight ternary fixed points we also calculate the number of intersections
between two chains placed at a fixed distance, including the two halves of a block-copolymer. The analysis of these systems
confirms the interpretation of the different contributions to the number of intersections in a single chain. Due to the highly
nontrivial character of the correlations in a polymer chain the correction exponents in both cases however are different.
None of the results can be extracted from any Flory-type estimate.
Received: 1 April 1997 / Revised: 24 October 1997 /
Accepted: 29 January 1998 相似文献
10.
A microscopic insight of interfacial spallation and recombination behaviors at multilayer thin-film interface induced by incident femtosecond pulsed laser is presented in this paper. Such two different aforementioned behaviors are investigated via the thermodynamic trajectories obtained by using standard Lennard-Jones (L-J) molecular dynamics (MD) simulation. Based on the simulation results, the interfacial damages of multilayer thin film are dominated by a critical threshold that induces an extraordinary expansive dynamics and phase transitions leading to the structural softened and tensile spallation at interface. The critical damage threshold is evaluated at around 8.5 J/m2 which governs the possible occurrence of two different regimes, i.e. interfacial spallaiton and recombination. In interfacial damage region, quasi-isothermal thermodynamic trajectories can be observed after the interfacial spallation occurs. Moreover, the result of thermodynamic trajectories analyses indicates that, the relaxation of pressure wave may cause the over-heated interfacial zone to reduce volumetric density, thus leading to structural softness and even weaken interfacial structural strength. The crucial effect leading to the phenomenon of low tension spallation is identified. 相似文献
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Hans-Karl Janssen 《Zeitschrift für Physik B Condensed Matter》1995,97(2):239-245
By methods of renormalized field theory we show that generically the multicritical behavior of the sol-gel transition at the consolute point is dominated by a fixed point symmetry which is higher than the symmetry of the original Hamiltonian. In general, this leads to Ising-like behavior of all fluctuations. We show in particular that the Fisher exponent
P
of the percolation field coincides with the corresponding exponent
I
of Ising fields. We perform a preliminary stability analysis which indicates that the higher symmetry is not broken in the physical 3-dimensional case.Dedicated to Professor Herbert Wagner on the occasion of his 60th birthday 相似文献
13.
The exact renormalization group approach (ERG) is developed for the case of pure fermionic theories by deriving a Grassmann version of the ERG equation and applying it to the study of fixed point solutions and critical exponents of the two-dimensional chiral Gross-Neveu model. An approximation based on the derivative expansion and a further truncation in the number of fields is used. Two solutions are obtained analytically in the limit N → ∞, with N being the number of fermionic species. For finite N some fixed point solutions, with their anomalous dimensions and critical exponents, are computed numerically. The issue of separation of physical results from the numerous spurious ones is discussed. We argue that one of the solutions we find can be identified with that of Dashen and Frishman, whereas the others seem to be new ones. 相似文献
14.
We address the problem of a Luttinger liquid with a scatterer that allows for both coherent and incoherent scattering channels. The asymptotic behavior at zero temperature is governed by a new stable fixed point: A Goldstone mode dominates the low energy dynamics, leading to universal behavior. This limit is marked by equal probabilities for forward and backward scattering. Notwithstanding this nontrivial scattering pattern, we find that the shot noise as well as cross-current correlations vanish. We thus present a paradigmatic picture of an impurity in the Luttinger model, alternative to the Kane-Fisher picture. 相似文献
15.
Investigation of the Potts Model on Triangular Lattices by the Second Renormalization of Tensor Network States 下载免费PDF全文
We employ the second renormalization group method of tensor-network states to investigate thermodynamic properties of the ferromagnetic and antiferromagnetic Potts model on triangular lattices. From the temperature dependence of the internal energy and the specific heat, both the critical temperatures and critical exponents are evaluated. For the q = 3 antiferromagnetic Potts model, the critical temperature is found to be Tc = 0.627163±0.000003, which is at least one order of magnitude more accurate than that obtained by other methods. 相似文献
16.
Microtubule-associated proteins (MAPs) are important proteins in cells. They can regulate the organization, dynamics and function of microtubules. We measure the binding force between microtubule and a new plant MAP, i.e. AtMAP65-1, by dual-optical tweezers. The force is obtained to be 14.6 ± 3.5 pN from the data statistics and analysis. This force measurement is helpful to understand the function and mechanism of MAPs from the mechanical point of view and lays the groundwork for future measurements of the mechanical properties of other biological macro-molecules. 相似文献
17.
Ümüt Temizer Ersin Kantar Mustafa Keskin Osman Canko 《Journal of magnetism and magnetic materials》2008
We study, within a mean-field approach, the stationary states of the kinetic Blume–Emery–Griffiths model with repulsive biquadratic coupling under the presence of a time-varying (sinusoidal) magnetic field. We employ the Glauber-type stochastic dynamics to construct set of dynamic equations of motion. The behavior of the time dependence of the order parameters and the behavior of the average order parameters in a period, which is also called the dynamic order parameters, as functions of the reduced temperature are investigated. The dynamic phase transition points are calculated and phase diagrams are presented in the reduced magnetic field amplitude and reduced temperature plane. The dynamical transition from one regime to the other can be of first- or second order depending on the region in the phase diagram. According to the values of the crystal field interaction or single-ion anisotropy constant and biquadratic exchange constant, we find 20 fundamental types of phase diagrams which exhibit many dynamic critical points, such as tricritical points, zero-temperature critical points, double critical end points, critical end point, triple point and multicritical point. Moreover, besides a disordered and ordered phases, seven coexistence phase regions exist in the system. 相似文献
18.
J. M. Luck A. Mehta 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(4):429-451
Granular media jam into a panoply of metastable states.
The way in which these states are achieved depends on the nature
of local and global constraints on grains; here we investigate this issue by means of a non-equilibrium stochastic model of
a hindered granular column near its jamming limit. Grains feel the constraints of grains
above and below them differently, depending on their position.
A rich phase diagram with four dynamical phases (ballistic, activated, logarithmic and glassy) is revealed. The statistics
of the jamming time and of the metastable states reached as attractors of the zero-temperature dynamics
is investigated in each of these phases. Of particular interest is the glassy phase, where intermittency and a strong deviation
from Edwards' flatness are manifest. 相似文献
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20.
In this paper, we study the multicritical behavior of the Ginzburg-Landau model in a O(n1)⊕O(n2)-symmetric version containing (n1/2+n2/2)-complex order parameters coupled to a gauge field. We develop the RG analysis at a one-loop approximation in the context of the ?-expansion approach. The beta functions are obtained, and in the case of equal couplings between the two scalar fields and the gauge field and n1=n2=n/2, the infrared stability of the fixed points is discussed. It is found that the charged infrared-stable fixed point exists for n>393.2. Calculations of the relevant critical exponents are also carried out. 相似文献