arXiv subjects

Javier Moreno-Gordo

Publications and source records attributed to Javier Moreno-Gordo.

3 recordsLinked to original sources

arXiv2024

Small field chaos in spin glasses: universal predictions from the ultrametric tree and comparison with numerical simulations

We study the chaotic behavior of the Gibbs state of spin-glasses under the application of an external magnetic field, in the crossover region where the field intensity scales proportional to $1/\sqrt{N}$, being $N$ the system size. We show that Replica Symmetry Breaking (RSB) theory provides universal predictions for chaotic behavior: they depend only on the zero-field overlap probability function $P(q)$ and are independent of other features of the system. Using solely $P(q)$ as input we can analytically predict quantitatively the statistics of the states in a small field. In the infinite volume limit, each spin-glass sample is characterized by an infinite number of states that have a tree-like structure. We generate the corresponding probability distribution through efficient sampling using a representation based on the Bolthausen-Sznitman coalescent. In this way, we can compute quantitatively properties in the presence of a magnetic field in the crossover region, the overlap probability distribution in the presence of a small field and the degree of decorrelation as the field is increased. To test our computations, we have simulated the Bethe lattice spin glass and the 4D Edwards-Anderson model, finding in both cases excellent agreement with the universal predictions.

cond-mat.dis-nn↗

arXiv2024

Evidence of a second-order phase transition in the six-dimensional Ising spin glass in a field

The very existence of a phase transition for spin glasses in an external magnetic field is controversial, even in high dimensions. We carry out massive simulations of the Ising spin-glass in a field, in six dimensions (which, according to classical -- but not generally accepted -- field-theoretical studies, is the upper critical dimension). We obtain results compatible with a second-order phase transition and estimate its critical exponents for the simulated lattice sizes. The detailed analysis performed by other authors of the replica symmetric Hamiltonian, under the hypothesis of critical behavior, predicts that the ratio of the renormalized coupling constants remain bounded as the correlation length grows. Our numerical results are in agreement with this expectation.

cond-mat.dis-nn↗

arXiv2021

Deepening the knowledge of Spin Glasses: Metastate, Off-equilibrium phenomena and Temperature Chaos

This thesis pretends to be another step in the development of numerical research in disordered systems. Specifically, we will focus on spin glasses which have demonstrated to be a fertile field from both, experimental and theoretical approaches. Throughout this thesis, we will discuss a variety of interesting phenomenons and we will also open new avenues to previously unexplored effects in the context of spin glasses. However, without a doubt, the leitmotiv conducting this thesis is the role of numerical simulations as a valuable tool to explore spin-glass physics. This thesis is organized into five different parts. The first part, containing the Chapter 1, is focused on introducing the spin glasses to the reader. The second part, containing the Chapter 2, is dedicated to discussing the metastate. The third part, shaped by the Chapter 3 and Chapter 4, is devoted to studying the off-equilibrium dynamics in spin glasses. Specifically, Chapter 3 is focused on discussing the growth of the coherence length in spin glasses, a key quantity that characterizes the off-equilibrium evolution of those systems. In Chapter 4 we will discuss an interesting phenomenon: the Mpemba effect. The fourth part, containing the Chapter 5, Chapter 6 and Chapter 7 is devoted to study the Temperature Chaos phenomenon in spin glasses. In Chapter 5 we introduce the main historical results on Temperature Chaos, from its origins to the last steps. In Chapter 6 we study equilibrated spin glasses and we characterize the Temperature Chaos from a static and a dynamical point of view. In Chapter 7 we tackle the problem of characterizing Temperature Chaos in off-equilibrium dynamics. The fifth and last part of the main body of the thesis corresponds to the conclusions.

cond-mat.dis-nn↗