arXiv subjects

E. A. Jagla

Publications and source records attributed to E. A. Jagla.

At least 19 recordsLinked to original sources

arXiv2026

Global Oscillations in Depinning Models with Aging

We propose a model that extends the standard depinning paradigm by incorporating an aging mechanism into the local pinning force. This favors oscillations between a stuck state of large pinning, and a slipping state of smaller pinning. We show that for mean field interactions between sites this mechanism can lead to the appearance of ``king avalanches" and global instabilities, producing a global oscillatory stick-slip stress regime. We construct the phase diagram for this mean field case and identify regions of smooth dynamics, pure stick-slip, and bistability. Crucially, when considering two-dimensional systems with short-range interactions we find that states of global stress oscillation persist, but in contrast to the mean field case, no system-size avalanches appear. Instead, we observe alternating temporal intervals of larger and lower avalanche activity that correlate with the stress oscillations.

cond-mat.stat-mech↗

arXiv2025

Discontinuous depinning/yielding transition of elastic manifolds with tailored internal elasticity

We consider elastic manifolds evolving on disordered energy potentials under the action of an external uniform driving. This scenario includes the cases of {\em depinning} and {\em yielding}, which provide paradigmatic examples of out of equilibrium phase transitions. In both cases, velocity of the manifold is zero at low driving force, and increases smoothly when a critical driving is exceeded,defining a continuous flow-curve for these systems. We show that when more general forms of the manifold elasticity are considered, the flow curve may become reentrant, and the transition hysteretic, or discontinuous. This constitutes a novel scenario for a discontinuous transition out of equilibrium.

cond-mat.stat-mech↗

arXiv2024

On the origin of filamentary resistive switching in oxides-based memristive devices

The control and manipulation of filamentary resistive switching (FRS) is essential for practical applications in fields like non-volatile memories and neuromorphic computing. However, key aspects of the dynamics of conductive filament formation and their influence on device resistance remain incompletely understood. In this work we study FRS in binary oxides based memristors by investigating the dynamics of oxygen vacancies (OV) on a two dimensional lattice and their role in forming low-resistance paths that facilitate the transition between high and low global resistance states. We reveal that the mere formation of an OV percolation path is insufficient to induce a transition to a low-resistance state. Instead, an OV concentration exceeding a critical threshold across all sites in the filament is required to generate a low-resistivity conducting path. Furthermore, we simulate the impact of static defects -which block OV migration and would correspond to voids in real porous samples-, on filament formation. We show that there is a range of defect density values where OV percolate through the sample, leading to the formation of OV filaments, but conductive paths remain absent. Additionally, a small concentration of defects can reduce the final value of the low-resistance state, thereby increasing the ON-OFF ratio. These findings provide valuable insights into optimizing defective nanomaterials with memristive properties, which are crucial for advancing in-memory and neuromorphic computing technologies.

cond-mat.mes-hall↗

arXiv2023

From shear bands to earthquakes in a model granular material with contact aging

We perform molecular dynamics simulations of homogeneous athermal systems of poly-disperse soft discs under shear. For purely repulsive interactions between particles, and under a confining external pressure, a monotonous flow curve (strain rate vs. stress) starting at a critical yield stress is obtained, with deformation distributing uniformly in the system, on average. Then we add a short range attractive contribution to the interaction potential that increases its intensity as particles remain in contact for a progressively longer time, mimicking an aging effect into the system. In this case the flow curve acquires a reentrant behavior, namely, a region of negative slope. Within this region the deformation is seen to localize in a shear band with a well defined width that decreases as the global strain rate does. At very low strain rates the shear band becomes very thin and deformation acquires a prominent stick-slip behavior. This regime can be described as the system possessing a fault in which deformation occurs with the phenomenology that characterizes earthquakes. In this way the system we are analyzing connects a regime of uniform deformation at large strain rates, a localized deformation regime in the form of shear bands at intermediate stain rates, and seismic phenomena at very low strain rate. The unifying ingredient of this phenomenology is the existence of a reentrant flow curve, originated in the aging mechanisms present in the model.

cond-mat.soft↗

arXiv2023

Quasi-static deformation of yield stress materials: homogeneous or localized?

We analyze a mesoscopic model of a shear stress material with a three dimensional slab geometry, under an external quasistatic deformation of a simple shear type. Relaxation is introduced in the model as a mechanism by which an unperturbed system achieves progressively mechanically more stable configurations. Although in all cases deformation occurs via localized plastic events (avalanches) we find qualitatively different behavior depending on the degree of relaxation in the model. For no or low relaxation yielding is homogeneous in the sample, and even the largest avalanches become negligible in size compared with the system size (measured as the thickness of the slab $L_z$) when this is increased. On the contrary, for high relaxation the deformation localizes in an almost two dimensional region where all avalanches occur. Scaling analysis of the numerical results indicates that in this case the linear size of the largest avalanches is comparable with $L_z$ even when this becomes very large. We correlate the two scenarios with a qualitative difference in the flow curve of the system in the two cases, which is monotonous in the first case, or of the velocity weakening type in the second case.

cond-mat.soft↗

arXiv2022

Down-hill creep of a granular material under expansion/contraction cycles

We investigate the down-hill creep of a layer of granular material on a slope caused by an oscillatory variation of the size of the particles. The material is modeled as an athermal two dimensional polydisperse system of soft disks under the action of gravity. The slope angle is below the critical rest angle and therefore the system reaches an equilibrium configuration under static external conditions. However, under a protocol in which particles slowly change size in a quasistatic oscillatory way the system is observed to creep down in a synchronized way with the oscillation. We measure the creep advance per cycle as a function of the slope angle and the degree of change in particle size. In addition, we consider a situation in which the particle size oscillation amplitude decreases with depth, as it may be argued to occur in the case of a granular soil in an inclined terrain. In this case creep profiles that are maximum at the surface and smoothly vanish with depth are obtained, as it is observed to occur in the field.

cond-mat.soft↗

arXiv2022

Volume-shear coupling in a mesoscopic model of amorphous materials

We present a two-dimensional mesoscopic model of a yield stress material that includes the possibility of local volume fluctuations coupled to shear, in such a way that the shear strength of the material decreases as the local density decreases. The model reproduces a number of effects well known in the phenomenology of this kind of materials. Particularly, we find that: the volume of the sample increases as the deformation rate increases; shear bands are no longer oriented at 45 $^\circ$ with respect to the principal axis of the applied stress (as in the absence of volume-shear coupling); homogeneous deformation becomes unstable at low enough deformation rates if volume-shear coupling is strong enough. We also analyze the implications of this coupling in the context of out of equilibrium shear bands appearing for instance in metallic glasses.

cond-mat.mtrl-sci↗

arXiv2021

Discontinuous yielding transition of amorphous materials with low bulk modulus

The yielding transition of amorphous materials is studied with a two-dimensional Hamiltonian model that allows both shear and volume deformations. The model is investigated as a function of the relative value of the bulk modulus $B$ with respect to the shear modulus $μ$. When the ratio $B/μ$ is small enough, the yielding transition becomes discontinuous, yet reversible. If the system is driven at constant strain rate in the coexistence region, a spatially localized shear band is observed while the rest of the system remains blocked. The crucial role of volume fluctuations in the origin of this behavior is clarified in a mean field version of the model.

cond-mat.soft↗

arXiv2020

Thermally rounded depinning of an elastic interface on a washboard potential

The thermal rounding of the depinning transition of an elastic interface sliding on a washboard potential is studied through analytic arguments and very accurate numerical simulations. We confirm the standard view that well below the depinning threshold the average velocity can be calculated considering thermally activated nucleation of forward moving defects. However, we find that the straightforward extension of this analysis to near or above the depinning threshold does not fully describe the physics of the thermally assisted motion. In particular, we find that exactly at the depinning point the average velocity does not follow a pure power-law of the temperature as naively expected by the analogy with standard phase transitions but presents subtle logarithmic corrections. We explain the physical mechanisms behind these corrections and argue that they are non-peculiar collective effects which may also apply to the case of interfaces sliding on uncorrelated disordered landscapes.

cond-mat.dis-nn↗

arXiv2019

Modeling plasticity of amorphous composites: Scalar is not enough

We use a continuous mesoscopic model to address the yielding properties of plastic composites, formed by a host material and inclusions with different elastic and/or plastic properties. We investigate the flow properties of the composed material under a uniform externally applied deviatoric stress. We show that due to the heterogeneities induced by the inclusions, a scalar modeling in terms of a single deviatoric strain of the same symmetry than the externally applied deformation gives inaccurate results. A realistic modeling must include all possible shear deformations. Implementing this model in a two-dimensional system we show that the effect of harder inclusions is very weak up to relatively high concentrations. For softer inclusions instead, the effect is much stronger, even a small concentration of inclusions affecting the form of the flow curve and the critical stress. We also present the details of a full three dimensional simulation scheme, and obtain the corresponding results, both for harder and softer inclusions.

cond-mat.stat-mech↗

arXiv2019

Criticality in elastoplastic models of amorphous solids with stress-dependent yielding rates

We analyze the behavior of different elastoplastic models approaching the yielding transition. We propose two kind of rules for the local yielding events: yielding occurs above the local threshold either at a constant rate or with a rate that increases as the square root of the stress excess. We establish a family of "static" universal critical exponents which do not depend on this dynamic detail of the model rules: in particular, the exponents for the avalanche size distribution $P(S)\sim S^{-τ_S}f(S/L^{d_f})$ and the exponents describing the density of sites at the verge of yielding, which we find to be of the form $P(x)\simeq P(0) + x^θ$ with $P(0)\sim L^{-a}$ controlling the extremal statistics. On the other hand, we discuss "dynamical" exponents that are sensitive to the local yielding rule details. We find that, apart form the dynamical exponent $z$ controlling the duration of avalanches, also the flowcurve's (inverse) Herschel-Bulkley exponent $β$ ($\dotγ\sim(σ-σ_c)^β$) enters in this category, and is seen to differ in $\frac12$ between the two yielding rate cases. We give analytical support to this numerical observation by calculating the exponent variation in the Hébraud-Lequeux model and finding an identical shift. We further discuss an alternative mean-field approximation to yielding only based on the so-called Hurst exponent of the accumulated mechanical noise signal, which gives good predictions for the exponents extracted from simulations of fully spatial models.

cond-mat.dis-nn↗

arXiv2019

Elastic interfaces on disordered substrates: From mean-field depinning to yielding

We consider a model of an elastic manifold driven on a disordered energy landscape, with generalized long range elasticity. Varying the form of the elastic kernel by progressively allowing for the existence of zero-modes, the model interpolates smoothly between mean field depinning and finite dimensional yielding. We find that the critical exponents of the model change smoothly in this process. Also, we show that in all cases the Herschel-Buckley exponent of the flowcurve depends on the analytical form of the microscopic pinning potential. This is a compelling indication that within the present elastoplastic description yielding in finite dimension $d\geq 2$ is a mean-field transition.

cond-mat.dis-nn↗

arXiv2018

On the critical region of long-range depinning transitions

The depinning transition of elastic interfaces with an elastic interaction kernel decaying as $1/r^{d+σ}$ is characterized by critical exponents which continuously vary with $σ$. These exponents are expected to be unique and universal, except in the fully coupled ($-d<σ\le 0$) limit, where they depend on the "smooth" or "cuspy" nature of the microscopic pinning potential. By accurately comparing the depinning transition for cuspy and smooth potentials in a specially devised depinning model, we explain such peculiar limit in terms of the vanishing of the critical region for smooth potentials, as we decrease $σ$ from the short-range ($σ\geq 2$) to the fully coupled case. Our results have practical implications for the determination of critical depinning exponents and identification of depinning universality classes in concrete experimental depinning systems with non-local elasticity, such as contact lines of liquids and fractures.

cond-mat.dis-nn↗

arXiv2018

On the critical exponents of the yielding transition of amorphous solids

We investigate numerically the yielding transition of a two dimensional model amorphous solid under external shear. We use a scalar model in terms of values of the total local strain, that we derive from the full (tensorial) description of the elastic interactions in the system, in which plastic deformations are accounted for by introducing a stochastic "plastic disorder" potential. This scalar model is seen to be equivalent to a collection of Prandtl-Tomlinson particles, which are coupled through an Eshelby quadrupolar kernel. Numerical simulations of this scalar model reveal that the strain rate vs stress curve, close to the critical stress, is of the form $\dotγ\sim (σ-σ_c)^β$. Remarkably, we find that the value of $β$ depends on details of the microscopic plastic potential used, confirming and giving additional support to results previously obtained with the full tensorial model. %\cite{Jagla_Yiel}. To rationalize this result, we argue that the Eshelby interaction in the scalar model can be treated to a good approximation in a sort of "dynamical" mean field, which corresponds to a Prandtl-Tomlinson particle that is driven by the applied strain rate in the presence of a stochastic noise generated by all other particles. The dynamics of this Prandtl-Tomlinson particle displays different values of the $β$ exponent depending on the analytical properties of the microscopic potential, thus giving support to the results of the numerical simulations. Moreover, we find that other critical exponents that depend on details of the dynamics show also a dependence with the form of the disorder, while static exponents are independent of the details of the disorder. Finally, we show how our scalar model relates to other elastoplastic models and to the widely used mean field version known as the Hébraud-Lequeux model.

cond-mat.stat-mech↗

arXiv2017

Elasto-plastic models of the yielding transition with stress-dependent transition rates

Elasto-plastic models are among the most successful ways to study the critical properties of the plastic yielding transition of amorphous solids. Typically these models are studied under a condition of constant transition rates from one plastic configuration to another, and in this form they predict the existence of well defined critical exponents that display universality, in the same sense that in standard equilibrium phase transitions. I show however that very naturally the transition rates must not be taken as a constant, but dependent of the local stress excess above the critical value. This modification in the model is seen to affect the values of some of the exponents of the transition, concretely, of the dynamical exponents that are related to the speed at which the system is driven. I argue about the reason for this dependence, claiming that it is due to the quasi-mean field nature of the plastic yielding transition originated in the fact that elastic interactions are long range.

cond-mat.stat-mech↗

arXiv2017

The Prandtl-Tomlinson model of friction with stochastic driving

We consider the classical Prandtl-Tomlinson model of a particle moving on a corrugated potential, pulled by a spring. In the usual situation in which pulling acts at constant velocity $\dotγ$, the model displays an average friction force $σ$ that relates to $\dotγ$ (for small $\dotγ)$ as $\dotγ\sim (σ-σ_c)^β$, where $σ_c$ is a critical friction force. The possible values of $β$ are well known in terms of the analytical properties of the corrugated potential. We study here the situation in which the pulling has, in addition to the constant velocity term, a stochastic term of mechanical origin (i.e, the total driving is a function of $\dotγt$). We analytically show how this term modifies the force-velocity dependence close to the critical force, and give the value of $β$ in terms of the analytical properties of the corrugation potential and the scaling properties of the stochastic driving, encoded in the value of its Hurst exponent.

cond-mat.stat-mech↗

arXiv2017

Creep and thermal rounding close to the elastic depinning threshold

We study the slow stochastic dynamics near the depinning threshold of an elastic interface in a random medium by solving a particularly suited model of hopping interacting particles that belongs to the quenched-Edwards-Wilkinson depinning universality class. The model allows us to compare the cases of uniformly activated and Arrhenius activated hops. In the former case, the velocity accurately follows a standard scaling law of the force and noise intensity with the analog of the thermal rounding exponent satisfying a modified "hyperscaling" relation. For the Arrhenius activation, we find, both numerically and analytically, that the standard scaling form fails for any value of the thermal rounding exponent. We propose an alternative scaling incorporating logarithmic corrections that appropriately fits the numerical results. We argue that this anomalous scaling is related to the strong correlation between activated hops that, alternated with deterministic depinning-like avalanches, occur below the depinning threshold. We rationalize the spatiotemporal patterns by making an analogy of the present model in the near-threshold creep regime with some well-known models with extremal dynamics, particularly the Bak-Sneppen model.

cond-mat.dis-nn↗

arXiv2017

Different universality classes at the yielding transition of amorphous systems

We study the yielding transition of a two dimensional amorphous system under shear by using a mesoscopic elasto-plastic model. The model combines a full (tensorial) description of the elastic interactions in the system, and the possibility of structural reaccommodations that are responsible for the plastic behavior. The possible structural reaccommodations are encoded in the form of a "plastic disorder" potential, which is chosen independently at each position of the sample to account for local heterogeneities. We observe that the stress must exceed a critical value $σ_c$ in order for the system to yield. In addition, when the system yields a flow curve relating stress $σ$ and strain rate $\dotγ$ of the form $\dotγ\sim(σ-σ_c)^β$ is obtained. Remarkably, we observe the value of $β$ to depend on some details of the plastic disorder potential. For smooth potentials a value of $β\simeq 2.0$ is obtained, whereas for potentials obtained as a concatenation of smooth pieces a value $β\simeq 1.5$ is observed in the simulations. This indicates a dependence of critical behavior on details of the plastic behavior that has not been pointed out before. In addition, by integrating out non-essential, harmonic degrees of freedom, we derive a simplified scalar version of the model that represents a collection of interacting Prandtl-Tomlinson particles. A mean field treatment of this interaction reproduces the difference of $β$ exponents for the two classes of plastic disorder potentials, and provides values of $β$ that compare favorably with those found in the full simulations.

cond-mat.mtrl-sci↗