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Register a new userNontrivial maturation metastate-average state in a one-dimensional long-range Ising spin glass: above and below the upper critical range
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Understanding the low-temperature pure state structure of spin glasses remains an open problem in the field of statistical mechanics of disordered systems. Here we study Monte Carlo dynamics, performing simulations of the growth of correlations following a quench from infinite temperature to a temperature well below the spin-glass transition temperature $T_c$ for a one-dimensional Ising spin glass model with diluted long-range interactions. In this model, the probability $P_{ij}$ that an edge ${i,j}$ has nonvanishing interaction falls as a power-law with chord distance, $P_{ij}propto1/R_{ij}^{2sigma}$, and we study a range of values of $sigma$ with $1/2<sigma<1$. We consider a correlation function $C_{4}(r,t)$. A dynamic correlation length that shows power-law growth with time $xi(t)propto t^{1/z}$ can be identified in the data and, for large time $t$, $C_{4}(r,t)$ decays as a power law $r^{-alpha_d}$ with distance $r$ when $rll xi(t)$. The calculation can be interpreted in terms of the maturation metastate averaged Gibbs state, or MMAS, and the decay exponent $alpha_d$ differentiates between a trivial MMAS ($alpha_d=0$), as expected in the droplet picture of spin glasses, and a nontrivial MMAS ($alpha_d e 0$), as in the replica-symmetry-breaking (RSB) or chaotic pairs pictures. We find nonzero $alpha_d$ even in the regime $sigma >2/3$ which corresponds to short-range systems below six dimensions. For $sigma < 2/3$, the decay exponent $alpha_d$ follows the RSB prediction for the decay exponent $alpha_s = 3 - 4 sigma$ of the static metastate, consistent with a conjectured statics-dynamics relation, while it approaches $alpha_d=1-sigma$ in the regime $2/3<sigma<1$; however, it deviates from both lines in the vicinity of $sigma=2/3$.
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Statistical mechanical models with local interactions in $d>1$ dimension can be regarded as $d=1$ dimensional models with regular long range interactions. In this paper we study the critical properties of Ising models having $V$ sites, each having $z$ randomly chosen neighbors. For $z=2$ the model reduces to the $d=1$ Ising model. For $z= infty$ we get a mean field model. We find that for finite $z > 2$ the system has a second order phase transition characterized by a length scale $L={rm ln}V$ and mean field critical exponents that are independent of $z$.
In classical finite-range spin systems, especially those with disorder such as spin glasses, a low-temperature Gibbs state may be a mixture of a number of pure or ordered states; the complexity of the Gibbs state has been defined in the past roughly as the logarithm of this number, assuming the question is meaningful in a finite system. As non-trivial pure-state structure is lost in finite size, in a recent paper [Phys. Rev. E 101, 042114 (2020)] Holler and the author introduced a definition of the complexity of an infinite-size Gibbs state as the mutual information between the pure state and the spin configuration in a finite region, and applied this also within a metastate construction. (A metastate is a probability distribution on Gibbs states.) They found an upper bound on the complexity for models of Ising spins in which each spin interacts with only a finite number of others, in terms of the surface area of the region, for all $Tgeq 0$. In the present paper, the complexity of a metastate is defined likewise in terms of the mutual information between the Gibbs state and the spin configuration. Upper bounds are found for each of these complexities for general finite-range (i.e. short- or long-range, in a sense we define) mixed $p$-spin interactions of discrete or continuous spins (such as $m$-vector models), but only for $T>0$. For short-range models, the bound reduces to the surface area. For long-range interactions, the definition of a Gibbs state has to be modified, and for these models we also prove that the states obtained within the metastate constructions are Gibbs states under the modified definition. All results are valid for a large class of disorder distributions.
In this note we study metastability phenomena for a class of long-range Ising models in one-dimension. We prove that, under suitable general conditions, the configuration -1 is the only metastable state and we estimate the mean exit time. Moreover, we illustrate the theory with two examples (exponentially and polynomially decaying interaction) and we show that the critical droplet can be macroscopic or mesoscopic, according to the value of the external magnetic field.
Parisis formal replica-symmetry--breaking (RSB) scheme for mean-field spin glasses has long been interpreted in terms of many pure states organized ultrametrically. However, the early version of this interpretation, as applied to the short-range Edwards-Anderson model, runs into problems because as shown by Newman and Stein (NS) it does not allow for chaotic size dependence, and predicts non-self-averaging that cannot occur. NS proposed the concept of the metastate (a probability distribution over infinite-size Gibbs states in a given sample that captures the effects of chaotic size dependence) and a non-standard interpretation of the RSB results in which the metastate is non-trivial and is responsible for what was called non-self-averaging. Here we use the effective field theory of RSB, in conjunction with the rigorous definitions of pure states and the metastate in infinite-size systems, to show that the non-standard picture follows directly from the RSB mean-field theory. In addition, the metastate-averaged state possesses power-law correlations throughout the low temperature phase; the corresponding exponent $zeta$ takes the value $4$ according to the field theory in high dimensions $d$, and describes the effective fractal dimension of clusters of spins. Further, the logarithm of the number of pure states in the decomposition of the metastate-averaged state that can be distinguished if only correlations in a window of size $W$ can be observed is of order $W^{d-zeta}$. These results extend the non-standard picture quantitatively; we show that arguments against this scenario are inconclusive.
In this paper we study bond percolation on a one-dimensional chain with power-law bond probability $C/ r^{1+sigma}$, where $r$ is the distance length between distinct sites. We introduce and test an order $N$ Monte Carlo algorithm and we determine as a function of $sigma$ the critical value $C_{c}$ at which percolation occurs. The critical exponents in the range $0<sigma<1$ are reported and compared with mean-field and $varepsilon$-expansion results. Our analysis is in agreement, up to a numerical precision $approx 10^{-3}$, with the mean field result for the anomalous dimension $eta=2-sigma$, showing that there is no correction to $eta$ due to correlation effects.
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