arXiv subjects

Ido Regev

Publications and source records attributed to Ido Regev.

At least 19 recordsLinked to original sources

arXiv2026

A Dynamical Mechanism for Irreversibility in Cyclically Driven Amorphous Solids

Amorphous solids subjected to athermal quasistatic oscillatory shear undergo a transition from periodic reversible dynamics to irreversible diffusive dynamics at yielding. How irreversibility arises in such deterministic, strongly dissipative systems remains unclear. Here we directly test the proposal that post-yield irreversibility originates from chaotic dynamics and exponential sensitivity to initial conditions. Contrary to this interpretation, perturbations initially contract rather than grow, even in the irreversible regime, with nearby trajectories remaining close for extended periods. Separation occurs only through rare branching events, after which the distance grows diffusively at the rate expected for independent trajectories. The waiting times to branching are exponentially distributed, defining a steady-state branching rate that vanishes in trained reversible limit cycles and becomes finite above yielding. A mean-field soft-spot model reproduces these branching statistics and reveals their microscopic origin: a small perturbation can reverse the activation order of two nearly degenerate plastic instabilities, altering the subsequent sequence of plastic events. These results show how local stability and global irreversibility can coexist in a dissipative many-body system and identify instability-selection-induced branching as a distinct dynamical route to irreversibility in driven amorphous solids.

cond-mat.soft↗

arXiv2025

Microscopic origin of shear bands in 2D amorphous solids from topological defects

The formation of shear bands in amorphous solids such as glasses has remained an open question in our understanding of condensed matter and amorphous materials. Unlike in crystals, well-defined topological defects such as dislocations have been elusive due to the lack of a periodic ordered background at the atomic level. Recently, topological defects have been identified in the displacement field and in the eigenvectors of amorphous solids. Recent work has suggested that shear bands in amorphous solids coincide with an alignment of vortex-antivortex dipoles, with alternating topological charge +1/-1. Here we numerically confirm this hypothesis by means of well-controlled simulations in 2D. Surprisingly, we show that a chain of topological defects (TDs) pre-exists the shear band and is visible already in the non-affine displacement field of the elastic regime. This chain is activated into a flow band concomitantly with the disappearance and possibly annihilation of a dipole at a distance from the TDs chain. The possible underlying mechanism is reminiscent of a soliton-like rarefaction pulse remotely activated by dipole annihilation as observed in superfluid Bose-Einstein condensates.

cond-mat.soft↗

arXiv2025

Burgers rings as topological signatures of Eshelby-like plastic events in glasses

Eshelby-like quadrupolar structures serve as the fundamental microscopic units for characterizing plastic instabilities in amorphous solids and play a crucial role in explaining their mechanical failure, including the formation of shear bands. However, identifying Eshelby-like plastic events in glasses remains challenging due to their inherent structural and dynamical complexity. In this work, we show that Eshelby-like structures can be precisely identified and localized using a topological invariant known as the continuous Burgers vector. By combining analytical and simulation techniques, we reveal the emergence of a topological Burgers ring around Eshelby plastic events, enabling the precise identification of their center of mass and capturing their orientation as well. This proposed method offers a clear and unambiguous framework to locate and characterize the plastic rearrangements that govern plasticity in glasses.

cond-mat.dis-nn↗

arXiv2024

Overlapping plastic events as a mechanism for irreversible dynamics in amorphous solids under oscillatory shear

The origin of the transition from asymptotically reversible to asymptotically irreversible response in amorphous solids subject to oscillatory shear is still unknown. It is known that the plastic events that result from shearing always involve localized particle rearrangements, but it is unclear why some are reversible while others are not. Here we show, using simulations and models, that overlaps between particle rearrangements caused by straining the solid in alternating directions can cause the response to become irreversible when they occur frequently. As the forcing amplitude increases, plastic events become more frequent, the number of such overlaps increases, and the probability of the system returning to previous states diminishes.

cond-mat.soft↗

arXiv2023

Memory switching due to thermal noise in amorphous solids subject to cyclic shear

The discovery that memory of particle configurations and plastic events can be stored in amorphous solids subject to oscillatory shear has spurred research into methods for storing and retrieving information from these materials. However, it is unclear to what extent the ability to store memory is affected by thermal fluctuations and other environmental noises, which are expected to be relevant in realistic situations. Here, we show that while memory has a long lifetime at low temperatures, thermal fluctuations eventually lead to a catastrophic loss of memory, resulting in the erasure of most or all of the stored information within a few forcing cycles. We observe that an escape from the memory-retaining state (limit cycle) is triggered by a change in the switching of plastic events, leading to a cascade of new plastic events that were not present in the original limit cycle. The displacements from the new plastic events change the particle configuration which leads to the loss of memory. We further show that the rate of escaping from a limit cycle increases in a non-Arrhenius manner as a function of temperature, and the probability of staying in a limit cycle decays exponentially with an increase in the shearing frequency. These results have important implications for memory storage since increasing the temperature offers a means of effectively erasing existing memories and allowing for the imprinting of new ones that can then be stored for a long time at low temperatures.

cond-mat.soft↗

arXiv2022

Perspective on Reversible to Irreversible Transitions in Periodic Driven Many Body Systems and Future Directions For Classical and Quantum Systems

Reversible to irreversible (R-IR) transitions arise in numerous periodically driven collectively interacting systems that, after a certain number of driving cycles, organize into a reversible state where the particle trajectories repeat, or remain irreversible with chaotic motion. R-IR transitions were first systematically studied for periodically sheared dilute colloids, and appear in a wide variety of both soft and hard matter systems, including amorphous solids, crystals, vortices in type-II superconductors, and magnetic textures. In some cases, the reversible transition is an absorbing phase transition with a critical divergence in the organization time scale. R-IR systems can store multiple memories and exhibit return point memory. We give an overview of R-IR transitions including recent advances in the field, and discuss how the general framework of R-IR transitions could be applied to a much broader class of periodically driven nonequilibrium systems, including soft and hard condensed matter systems, astrophysics, biological systems, and social systems. Some likely candidate systems are commensurate-incommensurate states, systems exhibiting hysteresis or avalanches, and nonequilibrium pattern forming states. Periodic driving could be applied to hard condensed matter systems to see if R-IR transitions occur in metal-insulator transitions, semiconductors, electron glasses, electron nematics, cold atom systems, or Bose-Einstein condensates. R-IR transitions could also be examined in dynamical systems where synchronization or phase locking occurs. We discuss the use of complex periodic driving such as changing drive directions or multiple frequencies as a method to retain complex multiple memories. Finally, we describe features of classical and quantum time crystals that could suggest the occurrence of R-IR transitions in these systems.

cond-mat.stat-mech↗

arXiv2022

Mapping out the glassy landscape of a mesoscopic elastoplastic model

We develop a mesoscopic model to study the plastic behavior of an amorphous material under cyclic loading. The model is depinning-like and driven by a disordered thresholds dynamics which are coupled by long-range elastic interactions. We propose a simple protocol of "glass preparation" which allows us to mimic thermalisation at high temperature, as well as aging at vanishing temperature. Various levels of glass stabilities (from brittle to ductile) can be achieved by tuning the aging duration. The aged glasses are then immersed into a quenched disorder landscape and serve as initial configurations for various protocols of mechanical loading by shearing. The dependence of the plastic behavior upon monotonous loading is recovered. The behavior under cyclic loading is studied for different ages and system sizes. The size and age dependence of the irreversibility transition is discussed. A thorough characterization of the disorder-landscape is achieved through the analysis of the transition graphs, which describe the plastic deformation pathways under athermal quasi-static shear. In particular, the analysis of the stability ranges of the strongly connected components of the transition graphs reveals the emergence of a phase-separation like process associated with the aging of the glass. Increasing the age and hence stability of the initial glass, results in a gradual break-up of the landscape of dynamically accessible stable states into three distinct regions: one region centered around the initially prepared glass phase, and two additional regions, characterized by well-separated ranges of positive and negative plastic strains, each of which is accessible only from the initial glass phase by passing through the stress peak in the forward, respectively, backward shearing directions.

cond-mat.soft↗

arXiv2021

Cooperative effects driving the multi-periodic dynamics of cyclically sheared amorphous solids

Plasticity in amorphous materials, such as glasses, colloids, or granular materials, is mediated by local rearrangements called "soft spots". Experiments and simulations have shown that soft spots are two-state entities interacting via quadrupolar displacement fields generated when they switch states. When the system is subjected to cyclic strain driving, the soft spots can return to their original state after one or more forcing cycles. In this case, the system has periodic dynamics and will always repeat the same microscopic states. Here we focus on multi-periodic dynamics, i.e. dynamics that has periodicity larger than the periodicity of the drive, and use a graph-theoretical approach to analyze the dynamics obtained from numerical simulations. In this approach, mechanically stable configurations that transform purely elastically into each other over a range of applied strains, are represented by vertices, and plastic events leading from one stable configuration to the other, are represented by directed edges. An algorithm based on the graph topology and the displacement fields of the soft spots reveals that multi-periodic behavior results from the states of some soft spots repeating after more than one period and provides information regarding the mechanisms that allow for such dynamics. To better understand the physical mechanisms behind multi-periodicity, we use a model of interacting hysterons. Each hysteron is a simplified two-state element representing hysteretic soft-spot dynamics. We identify several mechanisms for multi-periodicity in this model, some involving direct interactions between multi-periodic hysterons and another resulting from cooperative dynamics involving several hysterons. These cooperative events are naturally more common when more hysterons are present, thus explaining why multi-periodicity is more prevalent at large drive amplitudes.

cond-mat.soft↗

arXiv2021

Topology of the energy landscape of sheared amorphous solids and the irreversibility transition

Recent experiments and simulations of amorphous solids plastically deformed by oscillatory drive have foundsurprising behavior - for small strain amplitudes the dynamics can be reversible, which is contrary to the usual notion of plasticity as an irreversible form of deformation. This reversibility allows the system to reach limit-cycles in which plastic events repeat indefinitely under the oscillatory drive. Reaching reversible limit-cycles, can take a large number of driving cycles and it was surmised that the plastic events encountered during the transient period are not encountered again and are thus irreversible. Using a graph representation of the stable configurations of the system and the plastic events connecting them, we show that the notion of reversibility is more subtle. We find that reversible plastic events are abundant, and that a large portion of the plastic events encountered during the transient period are actually reversible, in the sense that they can be part of a reversible deformation path. We observe that the transition graph can be decomposed into clusters of configurations that are connected by reversible transitions. These clusters are the strongly connected components of the graph and their sizes turn out to be power-law distributed. The largest of these are grouped in regions of reversibility, which in turn are confined by regions of irreversibility whose number proliferates at larger strains. Our results provide an explanation for the irreversibility transition - the divergence of the transient period at a critical forcing amplitude. Long transients result from transition between clusters of reversibility in a search for a cluster large enough to contain a limit-cycle of a specific amplitude. For large enough amplitudes, the search time becomes very large, since sizes of the limit cycles become incompatible with the sizes of the regions of reversibility.

cond-mat.soft↗

arXiv2019

Networks and Hierarchies: How Amorphous Materials Learn to Remember

We consider the slow and athermal deformations of amorphous solids and show how the ensuing sequence of discrete plastic rearrangements can be mapped onto a directed network. The network topology reveals a set of highly connected regions joined by occasional one-way transitions. The highly connected regions include hierarchically organized hysteresis cycles and sub-cycles. At small to moderate strains this organization leads to near-perfect return point memory. The transitions in the network can be traced back to localized particle rearrangements (soft-spots) that interact via Eshelby-type deformation fields. By linking topology to dynamics, the network representations provides new insights into the mechanisms that lead to reversible and irreversible behavior in amorphous solids.

cond-mat.soft↗

arXiv2019

Noise spectra in the reversible-irreversible transition in amorphous solids under oscillatory driving

We study the stress fluctuations in simulations of a two-dimensional amorphous solid under a cyclic drive. It is known that this system organizes into a reversible state for small driving amplitudes and remains in an irreversible state for high driving amplitudes, and that a critical driving amplitude separates the two regimes. Here we study the time series of the stress fluctuations below and above the reversible-irreversible transition. In the irreversible regime above the transition, the power spectrum of the stress fluctuations is broad and has a $1/f^α$ shape with $1< α<2$. We find that the low frequency noise power peaks near the stress at which dc yielding occurs, which is consistent with the behavior expected in systems undergoing a non-equilibrium phase transition.

cond-mat.soft↗

arXiv2017

Yield in Amorphous Solids: The Ant in the Energy Landscape Labyrinth

It has recently been shown that yield in amorphous solids under oscillatory shear is a dynamical transition from asymptotically periodic to asymptotically chaotic, diffusive dynamics. However, the type and universality class of this transition are still undecided. Here we show that the diffusive behavior of the vector of coordinates of the particles comprising an amorphous solid when subject to oscillatory shear, is analogous to that of a particle diffusing in a percolating lattice, the so-called "ant in the labyrinth" problem, and that yield corresponds to a percolation transition in the lattice. We explain this as a transition in the connectivity of the energy landscape, which affects the phase-space regions accessible to the coordinate vector for a given maximal strain amplitude. This transition provides a natural explanation to the observed limit-cycles, periods larger than one and diverging time-scales at yield.

cond-mat.soft↗

arXiv2013

Onset of Irreversibility and Chaos in Amorphous Solids Under Periodic Shear

An important aspect of the physics of amorphous solids is the onset of irreversible behavior usually associated with yield. Here we study amorphous solids under periodic shear using quasi-static molecular dynamics simulations and observe a transition from reversible to irreversible deformation at a critical strain amplitude. We find that for small strain amplitudes the system exhibits a noisy but repetitive limit-cycle, similar to return point memory \cite{sethna1993hysteresis}. However, for large strain amplitudes the behavior becomes chaotic (shows sensitivity to initial conditions) and thus irreversible. We show that the chaotic behavior is a result of the shear band instabilities that arise for large strains and the convective displacement fields they create.

cond-mat.soft↗

arXiv2012

Rheology and Shear Band Suppression in Particle and Chain Mixtures

Using numerical simulations, we consider an amorphous particle mixture which exhibits shear banding, and find that the addition of even a small fraction of chains strongly enhances the material strength, creating pronounced overshoot features in the stress-strain curves. The strengthening occurs in the case where the chains are initially perpendicular to the shear direction, leading to a suppression of the shear band. For large strain, the chains migrate to the region where a shear band forms, resulting in a stress drop. The alignment of the chains by the shear bands results in a Bauschinger-like effect for subsequent reversed shear. Many of these features are captured in a simple model of a single chain being pulled through a viscous material. Our results are also useful for providing insights into methods of controlling and strengthening granular materials against failure.

cond-mat.soft↗

arXiv2012

Effective Temperature Thermodynamics and the Glass Transition: Connecting Time-Scales

We propose a theory based on simple physical arguments that describes a non equilibrium steady-state by a temperature-like parameter (an "effective temperature"). We show how one can predict the effective temperature as a function of the temperature of the environment for a specific case of non-equilibrium behavior: radiation amorphization. The main idea that we present is that the amorphization process is inherently connected to the dynamical arrest that a liquid undergoes when it transforms into a glass. We suggest that similar arguments may hold also for the effective temperature under plastic deformation.

cond-mat.stat-mech↗

arXiv2011

Statistical Mechanics of the Anomalous Behavior of Tetrahedral Liquids

Tetrahedral liquids such as water and silica-melt show unusual thermodynamic behavior such as a density maximum and an increase in specific-heat when cooled to low temperatures. There is a debate in the literature whether these phenomena stem from a phase transition into a low-density and high-density liquid phases, which occur in the supercooled regime. Here we consider a model of tetrahedral liquids for which we construct a volume-constrained statistical mechanical theory which quantifies the local structure of the liquid. We compare the theory to molecular dynamics simulations and show that the theory can rationalize the simulations semi-quantitatively. We show that the anomalous density and specific heat behavior arise naturally from this theory without exhibiting a liquid-liquid phase-transition. We explain that this theory may or may not have a phase transition, depending on the volume and temperature dependence of the energy and entropy which are sensitive to small changes in the parameters of the model.

cond-mat.stat-mech↗

arXiv2009

Time Scales in the Theory of Elasto-Plasticity of Amorphous Solids

Developing a macroscopic theory of elasto-plasticity in amorphous solids calls for (i) identifying the relevant macro state-variables and (ii) discriminating the different time-scales which characterize these variables. In current theories it is assumed that the stress reaches its elasto-plastic steady state value on the same time-scale as the configurational variables (be they the configurational energy, configurational entropy or the effective temperature). By examining numerical simulations in two and three dimensions we show that this is generally not the case, the configurational degrees of freedom may reach the elasto-plastic steady state on the time scales which can be very different from the time scale of the stress. We provide a physical discussion to rationalize these findings.

cond-mat.stat-mech↗

arXiv2009

The Effective Temperature in Elasto-Plasticity of Amorphous Solids

An effective temperature $T_{\rm eff}$ which differs from the bath temperature is believed to play an essential role in the theory of elasto-plasticity of amorphous solids. The definition of a measurable $T_{\rm eff}$ in the literature on sheared solids suffers however from being connected to a fluctuation-dissipation theorem which is correct only in equilibrium. Here we introduce a natural definition of $T_{\rm eff}$ based on measurable structural features without recourse to any questionable assumption. The value of $T_{\rm eff}$ is connected, using theory and scaling concepts, to the flow stress and the mean energy that characterize the elasto-plastic flow.

cond-mat.stat-mech↗