tag:blogger.com,1999:blog-74489950795771511292018-03-06T02:32:54.305-08:00cond-mat.dis-nn - Disordered Systems & Neural NetworksSite for <a href="http://communitypeerreview.blogspot.com/">Community Peer Review</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.comBlogger1317125tag:blogger.com,1999:blog-7448995079577151129.post-23681993898536119182013-08-06T00:02:00.003-07:002013-08-06T00:02:10.144-07:001308.0734 (Christophe Chatelain)<h2 class="title"><a href="http://arxiv.org/abs/1308.0734">Griffiths phase and critical behavior of the 2D Potts models with<br /> long-range correlated disorder</a> [<a href="http://arxiv.org/pdf/1308.0734">PDF</a>]</h2>Christophe Chatelain<a name='more'></a><blockquote class="abstract">The $q$-state Potts model with a long-range correlated disorder is studied by means of large-scale Monte Carlo simulations for $q=2,4,8$ and 16. Evidence is given of the existence of a Griffiths phase, where the thermodynamic quantities display an algebraic Finite-Size Scaling, in a finite range of temperatures around the self-dual point. The critical exponents are shown to depend on both the temperature and the exponent of the algebraic decay of disorder correlations, but not on the number of states of the Potts model. The mechanism leading to the violation of hyperscaling relations is observed in the entire Griffiths phase.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0734">http://arxiv.org/abs/1308.0734</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-43370082701070105992013-08-06T00:02:00.001-07:002013-08-06T00:02:09.048-07:001308.0781 (S. M. Popoff et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0781">Coherent control of total transmission of light through disordered media</a> [<a href="http://arxiv.org/pdf/1308.0781">PDF</a>]</h2>S. M. Popoff, A. Goetschy, S. F. Liew, A. D. Stone, H. Cao<a name='more'></a><blockquote class="abstract">We demonstrate order of magnitude coherent control of the total transmission through a disordered slab by shaping the wavefront of the input light. To understand the effect of finite illumination area on the maximum values of total transmission, we develop a model based on random matrix theory that reveals the role of long-range correlations. Predictions are confirmed by numerical simulations and shed light on our experimental results.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0781">http://arxiv.org/abs/1308.0781</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-82549527653819269352013-08-05T00:01:00.001-07:002013-08-05T00:01:35.812-07:001308.0590 (Kun W. Kim et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0590">Semiclassical approach to 2d impurity bound states in Dirac systems</a> [<a href="http://arxiv.org/pdf/1308.0590">PDF</a>]</h2>Kun W. Kim, T. Pereg-Barnea, G. Refael<a name='more'></a><blockquote class="abstract">The goal of this paper is to provide an intuitive and useful tool for analyzing the impurity bound state problem. We develop a semiclassical approach and apply it to an impurity in two dimensional systems with parabolic or Dirac like bands. Our method consists of reducing a higher dimensional problem into a sum of one dimensional ones using the two dimensional Green functions as a guide. We then analyze the one dimensional effective systems in the spirit of the wave function matching method as in the standard 1d quantum model. We demonstrate our method on two dimensional models with parabolic and Dirac-like dispersion, with the later specifically relevant to topological insulators.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0590">http://arxiv.org/abs/1308.0590</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-32868072698834690222013-08-04T00:02:00.001-07:002013-08-04T00:02:28.278-07:001308.0045 (Kun W. Kim et al.)<h2 class="title"><a href="http://arxiv.org/abs/1308.0045">A non-perturbative expression for the transmission through a leaky<br /> chiral edge mode</a> [<a href="http://arxiv.org/pdf/1308.0045">PDF</a>]</h2>Kun W. Kim, Israel Klich, Gil Refael<a name='more'></a><blockquote class="abstract">Chiral edge modes of topological insulators and Hall states exhibit non-trivial behavior of conductance in the presence of impurities or additional channels. We will present a simple formula for the conductance through a chiral edge mode coupled to a disordered bulk. For a given coupling matrix between the chiral mode and bulk modes, and a Green function matrix of bulk modes in real space, the renormalized Green function of the chiral mode is expressed in closed form as a ratio of determinants. We demonstrate the usage of the formula in two systems: i) a 1d wire with random onsite impurity potentials for which we found the disorder averaging is made simpler with the formula, and ii) a quantum Hall fluid with impurities in the bulk for which the phase picked up by the chiral mode due to the scattering with the impurities can be conveniently estimated.</blockquote>View original: <a href="http://arxiv.org/abs/1308.0045">http://arxiv.org/abs/1308.0045</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-78548989695047499892013-08-01T00:31:00.001-07:002013-08-01T00:31:45.509-07:001307.8180 (Xiaojun Cheng et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.8180">Transmission eigenvalues in random media with surface reflection</a> [<a href="http://arxiv.org/pdf/1307.8180">PDF</a>]</h2>Xiaojun Cheng, Chushun Tian, Azriel Z. Genack<a name='more'></a><blockquote class="abstract">The impact of surface reflection on the statistics of transmission eigenvalues is a largely unexplored subject of fundamental and practical importance in statistical optics. Here, we develop a first-principles theory and confirm numerically that the distribution of transmission eigenvalues of diffusive waves exhibits a nonanalytic `transition' as the strength of surface reflection at one surface passes through a critical value while that at the other is fixed. Above the critical value, the highest transmission eigenvalue is strictly smaller than unity and decreases with increasing internal reflection. When the input and output surfaces are equally reflective, the highest transmission eigenvalue is unity and the transition disappears irrespective of the strength of surface reflection.</blockquote>View original: <a href="http://arxiv.org/abs/1307.8180">http://arxiv.org/abs/1307.8180</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-41349352026822577232013-07-31T00:17:00.007-07:002013-07-31T00:17:15.441-07:001307.7719 (Shankar Iyer et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.7719">Susceptibility at the Superfluid-Insulator Transition for<br /> One-Dimensional Disordered Bosons</a> [<a href="http://arxiv.org/pdf/1307.7719">PDF</a>]</h2>Shankar Iyer, David Pekker, Gil Refael<a name='more'></a><blockquote class="abstract">A pair of recent Monte Carlo studies have reported evidence for and against a crossover from weak to strong-disorder criticality in the one-dimensional dirty boson problem. The Monte Carlo analyses rely on measurement of two observables: the effective Luttinger parameter K_{eff} and the superfluid susceptibility chi. The former quantity was previously calculated analytically, using the strong-disorder renormalization group (SDRG), by Altman, Kafri, Polkovnikov, and Refael. Here, we use an extension of the SDRG framework to find a non-universal anomalous dimension eta_{sd} characterizing the divergence of the susceptibility with system size: chi ~ L^(2-eta_{sd}). We show that eta_{sd} obeys the hyperscaling relation eta_{sd} = 1/2K_{eff}. We also identify an important obstacle to measuring this exponent on finite-size systems and comment on the implications for numerics and experiments.</blockquote>View original: <a href="http://arxiv.org/abs/1307.7719">http://arxiv.org/abs/1307.7719</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-43524082391771405982013-07-31T00:17:00.005-07:002013-07-31T00:17:14.699-07:001307.7742 (E. Katzav et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.7742">Stability and roughness of tensile cracks in disordered materials</a> [<a href="http://arxiv.org/pdf/1307.7742">PDF</a>]</h2>E. Katzav, M. Adda-Bedia<a name='more'></a><blockquote class="abstract">We study the stability and roughness of propagating cracks in heterogeneous brittle two-dimensional elastic materials. We begin by deriving an equation of motion describing the dynamics of such a crack in the framework of Linear Elastic Fracture Mechanics, based on the Griffith criterion and the Principle of Local Symmetry. This result allows us to extend the stability analysis of Cotterell and Rice to disordered materials. In the stable regime we find stochastic crack paths. Using tools of statistical physics we obtain the power spectrum of these paths and their probability distribution function, and conclude they do not exhibit self-affinity. We show that a real-space fractal analysis of these paths can lead to the wrong conclusion that the paths are self-affine. To complete the picture, we unravel the systematic bias in such real-space methods, and thus contribute to the general discussion of reliability of self-affine measurements.</blockquote>View original: <a href="http://arxiv.org/abs/1307.7742">http://arxiv.org/abs/1307.7742</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-21675645602268568072013-07-31T00:17:00.003-07:002013-07-31T00:17:13.924-07:001307.7846 (Aurélien Decelle et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.7846">Belief-Propagation Guided Monte-Carlo Sampling</a> [<a href="http://arxiv.org/pdf/1307.7846">PDF</a>]</h2>Aurélien Decelle, Florent Krzakala<a name='more'></a><blockquote class="abstract">A Monte-Carlo algorithm for discrete statistical models that combines the full power of the Belief Propagation algorithm with the advantages of a detailed-balanced heat bath approach is presented. A sub-tree inside the factor graph is first extracted randomly; Belief Propagation is then used as a perfect sampler to generate a configuration on the tree given the boundary conditions and the procedure is iterated. This appoach is best adapted for locally tree like graphs, it is therefore tested on the hard cases of spin-glass models for random graphs demonstrating its state-of-the art status in those cases.</blockquote>View original: <a href="http://arxiv.org/abs/1307.7846">http://arxiv.org/abs/1307.7846</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-32222894957379012532013-07-31T00:17:00.001-07:002013-07-31T00:17:12.937-07:001307.8018 (Rajeev Singh et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.8018">Extreme variability in convergence to structural balance in frustrated<br /> dynamical systems</a> [<a href="http://arxiv.org/pdf/1307.8018">PDF</a>]</h2>Rajeev Singh, Subinay Dasgupta, Sitabhra Sinha<a name='more'></a><blockquote class="abstract">In many complex systems, the dynamical evolution of the different components can result in adaptation of the connections between them. We consider the problem of how a fully connected network of discrete-state dynamical elements which can interact via positive or negative links, approaches structural balance by evolving its links to be consistent with the states of its components. The adaptation process, inspired by Hebb's principle, involves the interaction strengths evolving in accordance with the dynamical states of the elements. We observe that in the presence of stochastic fluctuations in the dynamics of the components, the system can exhibit large dispersion in the time required for converging to the balanced state. This variability is characterized by a bimodal distribution, which points to an intriguing non-trivial problem in the study of evolving energy landscapes.</blockquote>View original: <a href="http://arxiv.org/abs/1307.8018">http://arxiv.org/abs/1307.8018</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-57203818860409118882013-07-30T00:04:00.009-07:002013-07-30T00:04:49.488-07:001307.7166 (Manal Al-Ali et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.7166">Monte-Carlo simulations of the dissipative random transverse-field Ising<br /> chain</a> [<a href="http://arxiv.org/pdf/1307.7166">PDF</a>]</h2>Manal Al-Ali, Thomas Vojta<a name='more'></a><blockquote class="abstract">We study the influence of Ohmic dissipation on the random transverse-field Ising chain by means of large-scale Monte-Carlo simulations. To this end, we first map the Hamiltonian onto a classical Ising model with long-range $1/\tau^2$ interaction in the time-like direction. We then apply the highly efficient cluster algorithm proposed by Luijten and Bl\"ote for system with long-range interactions. Our simulations show that Ohmic dissipation destroys the infinite-randomness quantum critical point of the dissipationless system. Instead, the quantum phase transition between the paramagnetic and ferromagnetic phases is smeared. We compare our results to recent predictions of a strong-disorder renormalization group approach, and we discuss generalizations to higher dimensions as well as experiments.</blockquote>View original: <a href="http://arxiv.org/abs/1307.7166">http://arxiv.org/abs/1307.7166</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-81044737784549941512013-07-30T00:04:00.007-07:002013-07-30T00:04:45.560-07:001307.7173 (Yasmine Meroz et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.7173">Memory Effects in the Electron Glass</a> [<a href="http://arxiv.org/pdf/1307.7173">PDF</a>]</h2>Yasmine Meroz, Yuval Oreg, Yoseph Imry<a name='more'></a><blockquote class="abstract">We investigate theoretically the slow non-exponential relaxation dynamics of the electron glass out of equilibrium, where a sudden change in carrier density reveals interesting memory effects. The self-consistent model of the dynamics of the occupation numbers in the system successfully recovers the general behavior found in experiments. Our numerical analysis is consistent with both the expected logarithmic relaxation and our understanding of how increasing disorder or interaction slows down the relaxation process, thus yielding a consistent picture of the electron glass. We also present a novel finite size "domino" effect where the connection to the leads affects the relaxation process of the electron glass in mesoscopic systems. This effect speeds up the relaxation process, and even reverses the expected effect of interaction; stronger interaction then leading to a faster relaxation.</blockquote>View original: <a href="http://arxiv.org/abs/1307.7173">http://arxiv.org/abs/1307.7173</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-52698467438554110702013-07-30T00:04:00.005-07:002013-07-30T00:04:44.578-07:001307.7532 (C. Wang et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.7532">Anti-Levitation in the Integer Quantum Hall Systems</a> [<a href="http://arxiv.org/pdf/1307.7532">PDF</a>]</h2>C. Wang, Y. Avishai, Y. Meir, X. R. Wang<a name='more'></a><blockquote class="abstract">Two-dimensional electron gas in the integer quantum Hall regime is investigated numerically by studying the dynamics of an electron hopping on a square lattice subject to a perpendicular magnetic field and random on-site energy with white noise distribution. Focusing on the lowest Landau band we establish an anti-levitation scenario of the extended states: As either the disorder strength $W$ increases or the magnetic field strength $B$ decreases, the energies of the extended states move below the Landau energies pertaining to a clean system. Moreover, for strong enough disorder, there is a disorder dependent critical magnetic field $B_c(W)$ below which there are no extended states at all. A general phase diagram in the $W-1/B$ plane is suggested with a line separating domains of localized and delocalized states.</blockquote>View original: <a href="http://arxiv.org/abs/1307.7532">http://arxiv.org/abs/1307.7532</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-46712914279304252772013-07-30T00:04:00.003-07:002013-07-30T00:04:41.646-07:001307.7658 (Daniel B. Larremore et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.7658">Inhibition guarantees ceaseless cortex network dynamics</a> [<a href="http://arxiv.org/pdf/1307.7658">PDF</a>]</h2>Daniel B. Larremore, Woodrow L. Shew, Shan Yu, Dietmar Plenz, Edward Ott, Francesco Sorrentino, Juan G. Restrepo<a name='more'></a><blockquote class="abstract">Proper function of diverse biological, social, and engineered networks requires a balance of competing influences. In the cerebral cortex, inhibitory neurons keep excitatory neurons in check and play a crucial role in sensory processing. Experiments suggest inhibition is required to maintain cortex network dynamics at the critical point of a phase transition at which neuronal avalanches occur, and further suggest criticality optimizes aspects of cortical information processing. We numerically and analytically investigate critical dynamics in a network model and discover a previously unappreciated consequence of inhibition: the greater the number of inhibitory nodes, the more likely network dynamics are to be intrinsically self-sustaining. In the cortex, ongoing intrinsic dynamics play a role in memory consolidation and learning. We identify critical avalanches and also predict an experimentally observable signature of criticality that we confirm with recordings from the cortex of two awake monkeys, suggesting inhibition confers both balance and ceaseless critical dynamics in the cortex.</blockquote>View original: <a href="http://arxiv.org/abs/1307.7658">http://arxiv.org/abs/1307.7658</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-53767933165005791952013-07-30T00:04:00.001-07:002013-07-30T00:04:40.726-07:001307.7665 (Stephan Ulrich et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.7665">Shear shocks in fragile networks</a> [<a href="http://arxiv.org/pdf/1307.7665">PDF</a>]</h2>Stephan Ulrich, Nitin Upadhyaya, Bas van Opheusden, Vincenzo Vitelli<a name='more'></a><blockquote class="abstract">A minimal model for studying the mechanical properties of amorphous solids is a disordered network of point masses connected by unbreakable springs. At a critical value of its mean connectivity, such a network becomes fragile: it undergoes a rigidity transition signaled by a vanishing shear modulus and transverse sound speed. We investigate analytically and numerically the linear and non-linear visco-elastic response of these fragile solids by probing how shear fronts propagate through them. Our approach, that we tentatively label shear front rheology, provides an alternative route to standard oscillatory rheology. In the linear regime, we observe at late times a diffusive broadening of the fronts controlled by an effective shear viscosity that diverges at the critical point. No matter how small the microscopic coefficient of dissipation, strongly disordered networks behave as if they were over-damped because energy is irreversibly leaked into diverging non-affine fluctuations. Close to the transition, the regime of linear response becomes vanishingly small: the tiniest shear strains generate strongly non-linear shear shock waves qualitatively different from their compressional counterparts in granular media. The inherent non-linearities trigger an energy cascade from low to high frequency components that keep the network away from attaining the quasi-static limit. This mechanism, reminiscent of acoustic turbulence, causes a super-diffusive broadening of the shock width.</blockquote>View original: <a href="http://arxiv.org/abs/1307.7665">http://arxiv.org/abs/1307.7665</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-7733285647951151532013-07-29T00:01:00.005-07:002013-07-29T00:01:29.073-07:001307.6891 (Michele Castellana)<h2 class="title"><a href="http://arxiv.org/abs/1307.6891">The Renormalization Group for Disordered Systems</a> [<a href="http://arxiv.org/pdf/1307.6891">PDF</a>]</h2>Michele Castellana<a name='more'></a><blockquote class="abstract">In this thesis we investigate the Renormalization Group (RG) approach in finite-dimensional glassy systems, whose critical features are still not well-established, or simply unknown. We focus on spin and structural-glass models built on hierarchical lattices, which are the simplest non-mean-field systems where the RG framework emerges in a natural way. The resulting critical properties shed light on the critical behavior of spin and structural glasses beyond mean field, and suggest future directions for understanding the criticality of more realistic glassy systems.</blockquote>View original: <a href="http://arxiv.org/abs/1307.6891">http://arxiv.org/abs/1307.6891</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-22085777359880807572013-07-29T00:01:00.003-07:002013-07-29T00:01:28.306-07:001307.6921 (Y. V. Pershin et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.6921">Memcapacitive neural networks</a> [<a href="http://arxiv.org/pdf/1307.6921">PDF</a>]</h2>Y. V. Pershin, M. Di Ventra<a name='more'></a><blockquote class="abstract">We show that memcapacitive (memory capacitive) systems can be used as synapses in artificial neural networks. As an example of our approach, we discuss the architecture of an integrate-and-fire neural network based on memcapacitive synapses. Moreover, we demonstrate that the spike-timing-dependent plasticity can be simply realized with some of these devices. Memcapacitive synapses are a low-energy alternative to memristive synapses for neuromorphic computation.</blockquote>View original: <a href="http://arxiv.org/abs/1307.6921">http://arxiv.org/abs/1307.6921</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-76633029105282993022013-07-29T00:01:00.001-07:002013-07-29T00:01:27.260-07:001307.6948 (Hai-Jun Zhou)<h2 class="title"><a href="http://arxiv.org/abs/1307.6948">The Feedback Vertex Set Problem: a Spin Glass Approach</a> [<a href="http://arxiv.org/pdf/1307.6948">PDF</a>]</h2>Hai-Jun Zhou<a name='more'></a><blockquote class="abstract">A feedback vertex set (FVS) of an undirected graph is a set of vertices that contains at least one vertex of each cycle of the graph. The feedback vertex set problem consists of constructing a FVS of size less than certain given value. This combinatorial optimization problem has many practical applications, but it can be extremely difficult to solve as it belongs to the nondeterministic polynomial-complete (NP-complete) class of worst-case computational complexity. In this paper we define a spin glass model for the FVS problem and then study this model on the ensemble of finite-connectivity random graphs. A key novelty of our model is that the global cycle constraints are represented through the local constraints on all the edges of the graph. After this mapping from the global cycle constraints to the local edge constraints, the FVS problem can then be treated by distributed message-passing procedures such as belief propagation. We demonstrate that the belief propagation-guided decimation algorithm based on our spin glass model is able to construct nearly optimal feedback vertex sets for single random graph instances. We also construct a spin glass model for the FVS problem on a directed graph. Our theoretical work may also shed light on designing suitable spin glass models for hard optimization problems with other global constraints.</blockquote>View original: <a href="http://arxiv.org/abs/1307.6948">http://arxiv.org/abs/1307.6948</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-86219426651227820792013-07-26T00:47:00.005-07:002013-07-26T00:47:20.729-07:001307.6613 (Arthur Lavarélo et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.6613">Magnetic responses of randomly depleted spin ladders</a> [<a href="http://arxiv.org/pdf/1307.6613">PDF</a>]</h2>Arthur Lavarélo, Guillaume Roux, Nicolas Laflorencie<a name='more'></a><blockquote class="abstract">The magnetic responses of a spin-1/2 ladder doped with non-magnetic impurities are studied using various methods and including the regime where frustration induces incommensurability. Several improvements are made on the results of the seminal work of Sigrist and Furusaki [J. Phys. Soc. Jpn. 65, 2385 (1996)]. Deviations from the Brillouin magnetic curve due to interactions are also analyzed. First, the magnetic profile around a single impurity and effective interactions between impurities are analyzed within the bond-operator mean-field theory and compared to density-matrix renormalization group calculations. Then, the temperature behavior of the Curie constant is studied in details. At zero-temperature, we give doping-dependent corrections to the results of Sigrist and Furusaki on general bipartite lattice and compute exactly the distribution of ladder cluster due to chain breaking effects. Using exact diagonalization and quantum Monte-Carlo methods on the effective model, the temperature dependence of the Curie constant is compared to a random dimer model and a real-space renormalization group scenario. Next, the low-part of the magnetic curve corresponding to the contribution of impurities is computed using exact diagonalization. The random dimer model is shown to capture the bulk of the curve, accounting for the deviation from the Brillouin response. At zero-temperature, the effective model prediction agrees relatively well with density-matrix renormalization group calculations. Finite-temperature effects are displayed within the effective model and for large depleted ladder models using quantum Monte-Carlo simulations. In all, the effect of incommensurability does not display a strong qualitative effect on both the magnetic susceptibility and the magnetic curve. Consequences for experiments on the BiCu2PO6 compound and other spin-gapped materials are briefly discussed.</blockquote>View original: <a href="http://arxiv.org/abs/1307.6613">http://arxiv.org/abs/1307.6613</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-75672640078572253782013-07-26T00:47:00.003-07:002013-07-26T00:47:20.005-07:001307.6746 (Fernando Gargiulo et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.6746">Topological Aspects of Charge-Carrier Transmission across Grain<br /> Boundaries in Graphene</a> [<a href="http://arxiv.org/pdf/1307.6746">PDF</a>]</h2>Fernando Gargiulo, Oleg V. Yazyev<a name='more'></a><blockquote class="abstract">We systematically investigate the transmission of charge carriers across the grain-boundary defects in polycrystalline graphene by means of the Landauer-B\"uttiker formalism within the tight-binding approximation. Calculations reveal a strong suppression of transmission at low energies upon decreasing the density of dislocations with the smallest Burger's vector ${\mathbf b}=(1,0)$. The observed transport anomaly is explained from the point of view of back-scattering due to localized states of topological origin. These states are related to the gauge field associated with all dislocations characterized by ${\mathbf b}=(n,m)$ with $n-m \neq 3q$ ($q \in \mathbb{Z}$). Our work identifies an important source of charge-carrier scattering caused by topological defects present in large-area graphene samples produced by chemical vapor deposition.</blockquote>View original: <a href="http://arxiv.org/abs/1307.6746">http://arxiv.org/abs/1307.6746</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-38381464722632583852013-07-26T00:47:00.001-07:002013-07-26T00:47:19.024-07:001307.6767 (E. A. A. Pogna et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.6767">Acoustic-like dynamics of amorphous drugs in the THz regime</a> [<a href="http://arxiv.org/pdf/1307.6767">PDF</a>]</h2>E. A. A. Pogna, C. Rodriguez-Tinoco, M. Krisch, J. Rodriguez-Viejo, T. Scopigno<a name='more'></a><blockquote class="abstract">The high frequency dynamics of Indomethacin and Celecoxib glasses has been investigated by inelastic x-ray scattering, accessing a momentum-energy region still unexplored in amorphous pharmaceuticals. We find evidence of phonon-like acoustic dynamics, and determine the THz behavior of sound velocity and acoustic attenuation. Connections with ordinary sound propagation are discussed, along with the relation between fast and slow degrees of freedom as represented by non-ergodicity factor and kinetic fragility, respectively.</blockquote>View original: <a href="http://arxiv.org/abs/1307.6767">http://arxiv.org/abs/1307.6767</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-30764739629333359202013-07-25T00:33:00.001-07:002013-07-25T00:33:25.295-07:001307.6359 (Davide Cellai et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.6359">Percolation in Multiplex Networks with Overlap</a> [<a href="http://arxiv.org/pdf/1307.6359">PDF</a>]</h2>Davide Cellai, Eduardo López, Jie Zhou, James P. Gleeson, Ginestra Bianconi<a name='more'></a><blockquote class="abstract">From transportation networks to complex infrastructures, and to social and communication networks, a large variety of systems can be described in terms of multiplexes formed by a set of nodes interacting through different networks (layers). Multiplexes may display an increased fragility with respect to the single layers that constitute them. However, so far the overlap of the links in different layers has been mostly neglected, despite the fact that it is an ubiquitous phenomenon in most multiplexes. Here we show that the overlap among layers can improve the robustness of interdependent multiplex systems and change the critical behavior of the percolation phase transition in a complex way.</blockquote>View original: <a href="http://arxiv.org/abs/1307.6359">http://arxiv.org/abs/1307.6359</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-63377605727560327182013-07-24T00:17:00.001-07:002013-07-24T00:17:03.519-07:001307.6138 (N. M. Chtchelkatchev et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.6138">Universality and quantization of the power to heat ratio in<br /> nano-granular systems</a> [<a href="http://arxiv.org/pdf/1307.6138">PDF</a>]</h2>N. M. Chtchelkatchev, A. Glatz, I. S. Beloborodov<a name='more'></a><blockquote class="abstract">We study heating and dissipation effects in granular nanosystems in the regime of weak coupling between the grains. We focus on the cotunneling regime and solve the heat-dissipation problem in an array of grains exactly. We show that the power to heat ratio has a universal quantized value, which is geometrically protected: it depends only on the number of grains.</blockquote>View original: <a href="http://arxiv.org/abs/1307.6138">http://arxiv.org/abs/1307.6138</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-77676834077402524132013-07-23T00:02:00.001-07:002013-07-23T00:02:35.674-07:001307.5430 (Lode Pollet)<h2 class="title"><a href="http://arxiv.org/abs/1307.5430">A review of Monte Carlo simulations for the Bose-Hubbard model with<br /> diagonal disorder</a> [<a href="http://arxiv.org/pdf/1307.5430">PDF</a>]</h2>Lode Pollet<a name='more'></a><blockquote class="abstract">We review the physics of the Bose-Hubbard model with disorder in the chemical potential focusing on recently published analytical arguments in combination with quantum Monte Carlo simulations. Apart from the superfluid and Mott insulator phases that can occur in this system without disorder, disorder allows for an additional phase, called the Bose glass phase. The topology of the phase diagram is subject to strong theorems proving that the Bose Glass phase must intervene between the superfluid and the Mott insulator and implying a Griffiths transition between the Mott insulator and the Bose glass. The full phase diagrams in 3d and 2d are discussed, and we zoom in on the insensitivity of the transition line between the superfluid and the Bose glass in the close vicinity of the tip of the Mott insulator lobe. We briefly comment on the established and remaining questions in the 1d case, and give a short overview of numerical work on related models.</blockquote>View original: <a href="http://arxiv.org/abs/1307.5430">http://arxiv.org/abs/1307.5430</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-10675028270126418162013-07-22T00:01:00.003-07:002013-07-22T00:01:35.280-07:001307.5154 (Adriano Barra et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.5154">Multi-species mean-field spin-glasses. Rigorous results</a> [<a href="http://arxiv.org/pdf/1307.5154">PDF</a>]</h2>Adriano Barra, Pierluigi Contucci, Emanuele Mingione, Daniele Tantari<a name='more'></a><blockquote class="abstract">We study a multi-species spin glass system where the density of each species is kept fixed at increasing volumes. The model reduces to the Sherrington-Kirkpatrick one for the single species case. The existence of the thermodynamic limit is proved for all densities values under a convexity condition on the interaction. The thermodynamic properties of the model are investigated and the annealed, the replica symmetric and the replica symmetry breaking bounds are proved using Guerra's scheme. The annealed approximation is proved to be exact under a high temperature condition. We show that the replica symmetric solution has negative entropy at low temperatures. We study the properties of a suitably defined replica symmetry breaking solution and we optimise it within a ziggurat ansatz. The generalized order parameter is described by a Parisi-like partial differential equation.</blockquote>View original: <a href="http://arxiv.org/abs/1307.5154">http://arxiv.org/abs/1307.5154</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0tag:blogger.com,1999:blog-7448995079577151129.post-74955623150154092072013-07-22T00:01:00.001-07:002013-07-22T00:01:34.395-07:001307.5247 (P. H. Lundow et al.)<h2 class="title"><a href="http://arxiv.org/abs/1307.5247">Critical exponents in Ising Spin Glasses</a> [<a href="http://arxiv.org/pdf/1307.5247">PDF</a>]</h2>P. H. Lundow, I. A. Campbell<a name='more'></a><blockquote class="abstract">Extensive simulations are made of the spin glass susceptibility and correlation length in five dimension Ising Spin Glasses (ISGs) with Gaussian and bimodal interaction distributions. Once the transition temperature is accurately established using a standard criterion, critical exponents and correction terms can be readily estimated by extrapolating measurements made in the thermodynamic limit regime. The data show that the critical exponents of the susceptibility $\gamma$ and of the correlation length $\nu$ depend on the form of the interaction distribution. This observation implies that quite generally critical exponents are not universal in ISGs.</blockquote>View original: <a href="http://arxiv.org/abs/1307.5247">http://arxiv.org/abs/1307.5247</a>C.P.R.http://www.blogger.com/profile/13598012384534951656noreply@blogger.com0