arXiv subjects

E. A. Jagla

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

At least 73 records · Page 4Linked to original sources

arXiv2003

Solid-solid volume collapse transitions are zeroth order

We present an exactly solvable non-linear elastic model of a volume collapse transition in an isotropic solid. Integrity of the lattice through the transition leads to an infinite-range density-density interaction, which drives classical critical behavior. Nucleation is forbidden within a pressure window leading to intrinsic hysteresis and an unavoidable discontinuity of the thermodynamic potential (zeroth order transition). The window shrinks with increasing temperature ending at a critical point at a temperature related to the shear modulus. Mixed phases behave non-extensively and show negative compressibility. We discuss the implications for Ce, SmS, and related systems.

cond-mat.str-el↗

arXiv2002

Boundary lubrication properties of materials with expansive freezing

We have performed molecular dynamics simulations of solid-solid contacts lubricated by a model fluid displaying many of the properties of water, particularly its expansive freezing. Near the region where expansive freezing occurs, the lubricating film remains fluid, and the friction force decreases linearly as the shear velocity is reduced. No sign of stick-slip motion is observed even at the lowest velocities. We give a simple interpretation of these results, and suggest that in general good boundary lubrication properties will be found in the family of materials with expansive freezing.

cond-mat↗

arXiv2002

Stable propagation of an ordered array of cracks during directional drying

We study the appearance and evolution of an array of parallel cracks in a thin slab of material that is directionally dried, and show that the cracks penetrate the material uniformly if the drying front is sufficiently sharp. We also show that cracks have a tendency to become evenly spaced during the penetration. The typical distance between cracks is mainly governed by the typical distance of the pattern at the surface, and it is not modified during the penetration. Our results agree with recent experimental work, and can be extended to three dimensions to describe the properties of columnar polygonal patterns observed in some geological formations.

cond-mat.mtrl-sci↗

arXiv2001

Sequential fragmentation: The origin of columnar quasi-hexagonal patterns

We present a model that explains the origin and predicts the statistical properties of columnar quasi-hexagonal crack patterns, as observed in the columnar jointing of basaltic lava flows. Irregular fractures appear at the surface of the material, induced by temperature gradients during cooling. At later times fractures penetrate into the material, and tend to form polygonal patterns. We show that this ordering can be described as a tendency to minimize an energy functional. Atomistic simulations confirm this interpretation. Numerical simulations based on a phenomenological implementation of this principle generate patterns that have remarkably good statistical agreement with real ones.

cond-mat.stat-mech↗

arXiv2001

Liquid-liquid equilibrium for monodisperse spherical particles

A system of identical particles interacting through an isotropic potential that allows for two preferred interparticle distances is numerically studied. When the parameters of the interaction potential are adequately chosen, the system exhibits coexistence between two different liquid phases (in addition to the usual liquid-gas coexistence). It is shown that this coexistence can occur at equilibrium, namely, in the region where the liquid is thermodynamically stable.

cond-mat↗

arXiv2001

Comment on "First order amorphous-amorphous transformation in silica"

In a recent letter (Phys. Rev. Lett. 84, 4629 (2000)), Lacks presents evidence of a first order amorphous-amorphous transition in silica at T=0. He calculates the free energy along a path of compression and successive decompression of a sample of 108 SiO2 units. The free energy of the two branches cross each other, and this is interpreted as evidence of a first order transition. We show that this conclusion does not follow from the shown data, since qualitatively the same phenomenology is obtained in a model where a first order transition does not exist.

cond-mat.mtrl-sci↗

arXiv2001

Low temperature properties of core-softened models: water vs. silica behavior

A core-softened model of a glass forming fluid is numerically studied in the limit of very low temperatures. The model shows two qualitatively different behaviors depending on the strength of the attraction between particles. For no or low attraction, the changes of density as a function of pressure are smooth, although hysteretic due to mechanical metastabilities. For larger attraction, sudden changes of density upon compressing and decompressing occur. This global mechanical instability is correlated to the existence of a thermodynamic first-order amorphous-amorphous transition. The two different behaviors obtained correspond qualitatively to the different phenomenology observed in silica and water.

cond-mat.stat-mech↗

arXiv2000

Fragile-strong transitions and polyamorphism in glass former fluids

A simple model of a glass former fluid, consisting of a bidisperse mixture of penetrable spheres is studied. The model shows a transition from fragile to strong behavior as temperature is reduced. This transition is driven by the competition between the two mechanisms that contribute to diffusivity in the model: collective rearrangement of particles (responsible for the fragile behavior), and individual particle motion (which gives rise to the strong behavior at low temperature). We also observe a maximum of diffusivity as a function of pressure that can be interpreted within the same framework. The connection between this behavior and polyamorphism is addressed.

cond-mat↗

arXiv1999

Surface defreezing of glasses

A glass surface may still flow below the bulk glass transition temperature, where the underlying bulk is frozen. Assuming the existence at T=T* of a bulk thermodynamical glass transition, we show that the glass-vapor interface is generally wetted by a liquid layer of thickness ~ -ln(T*-T) when T--> T*. Contrary to standard surface melting of crystals however, the integrated value of the diffusivity across the interface remains finite for T-->T*. Difference in shape induced by bulk and by surface flow is discussed as a possible means of experimental detection of surface defreezing.

cond-mat.mtrl-sci↗

arXiv1999

Can one have preroughening of vicinal surfaces?

We discuss the possibility that, besides roughening, a vicinal surface could display preroughening (PR), and consider the possible mechanisms for its promotion. Within the framework of a terrace-step-kink model, it turns out that a PR transition is possible, and could be induced by a short-range repulsion between parallel kinks along the same step or on adjacent steps, or even by some kind of extended range step-step repulsion. We discuss the possible relevance of this phenomenon to the anomalous roughening behaviour recently reported for Ag(115).

cond-mat.stat-mech↗

arXiv1999

A model for the fragile-to-strong transition in water

A model based on the existence of two different competing local structures in water is described. It is shown that it can explain the transition between fragile and strong behavior that supercooled water has around 220 K. The high temperature behavior is similar to that observed in standard fragile glass-formers. The strong behavior at low temperatures is associated with the existence of a remanent configurational entropy coming from the possibility of locally choosing between the two possible environments.

cond-mat.stat-mech↗

arXiv1999

Core-softened potentials and the anomalous properties of water

We study the phase diagram of a system of spherical particles interacting in three dimensions through a potential consisting of a strict hard core plus a linear repulsive shoulder at larger distances. The phase diagram (obtained numerically, and analytically in a limiting case) shows anomalous properties that are similar to those observed in water. Specifically, we find maxima of density and isothermal compressibility as a function of temperature, melting with volume contraction, and multiple stable crystalline structures. If in addition a long range attraction between the particles is included, the usual liquid-gas coexistence curve with its critical point is obtained. But more interestingly, a first order line in the metastable fluid branch of the phase diagram appears, ending in a new critical point, as it was suggested to occur in water. In this way the model provides a comprehensive, consistent and unified picture of most of the anomalous thermodynamical properties of water, showing that all of them can be qualitatively explained by the existence of two competing equilibrium values for the interparticle distance.

cond-mat.stat-mech↗

arXiv1998

Melting of Hard Cubes

The melting transition of a system of hard cubes is studied numerically both in the case of freely rotating cubes and when there is a fixed orientation of the particles (parallel cubes). It is shown that freelly rotating cubes melt through a first-order transition, whereas parallel cubes have a continuous transition in which positional order is lost but bond-orientational order remains finite. This is interpreted in terms of a defect-mediated theory of melting

cond-mat.stat-mech↗

arXiv1998

Minimum energy configurations of repelling particles in two dimensions

Geometrical arrangements of minimum energy of a system of identical repelling particles in two dimensions are studied for different forms of the interaction potential. Stability conditions for the triangular structure are derived, and some potentials not satisfying them are discussed. It is shown that in addition to the triangular lattice, other structures may appear (some of them with non-trivial unit cells, and non-equivalent positions of the particles) even for simple choices of the interaction. The same qualitative behavior is expected in three dimensions.

cond-mat.mtrl-sci↗

arXiv1998

Phase behavior of a system of particles with core collapse

The pressure-temperature phase diagram of a one-component system, with particles interacting through a spherically symmetric pair potential in two dimensions is studied. The interaction consists of a hard core plus an additional repulsion at low energies. It is shown that at zero temperature, instead of the expected isostructural transition due to core collapse occurring when increasing pressure, the system passes through a series of ground states that are not triangular lattices. In particular, and depending on parameters, structures with squares, chains, hexagons and even quasicrystalline ground states are found. At finite temperatures the solid-fluid coexistence line presents a zone with negative slope (which implies melting with decreasing in volume) and the fluid phase has a temperature of maximum density, similar to that in water.

cond-mat.stat-mech↗

arXiv1997

Complex phase diagram from simple interactions in a one-component system

The pressure-temperature phase diagram of a one-component system, with particles interacting through a spherically symmetric pair potential is studied. It is shown that if the pair potential allows for a discontinuous reduction of the volume of the system when pressure is increased (at zero temperature), then the phase diagram obtained has many ``water like'' characteristics. Among these characteristics the negative thermal expansion and expansion upon freezing in some range of pressure, and the existence of many different crystaline structures are clearly observable in numerical simulations. This implies that complex phase diagrams are not necessarily originated in complex microscopic interactions.

cond-mat.stat-mech↗

arXiv1997

Longitudinal and transverse dissipation in a simple model for the vortex lattice with screening

Transport properties of the vortex lattice in high temperature superconductors are studied using numerical simulations in the case in which the non-local interactions between vortex lines are dismissed. The results obtained for the longitudinal and transverse resistivities in the presence of quenched disorder are compared with the results of experimental measurements and other numerical simulations where the full interaction is considered. This work shows that the dependence on temperature of the resistivities is well described by the model without interactions, thus indicating that many of the transport characteristics of the vortex structure in real materials are mainly a consequence of the topological configuration of the vortex structure only. In addition, for highly anisotropic samples, a regime is obtained where longitudinal coherence is lost at temperatures where transverse coherence is still finite. I discuss the possibility of observing this regime in real samples.

cond-mat.supr-con↗

arXiv1996

The phase diagram of high-Tc's: Influence of anisotropy and disorder

We propose a phase diagram for the vortex structure of high temperature superconductors which incorporates the effects of anisotropy and disorder. It is based on numerical simulations using the three-dimensional Josephson junction array model. We support the results with an estimation of the internal energy and configurational entropy of the system. Our results give a unified picture of the behavior of the vortex lattice, covering from the very anysotropic BiSrCaCuO to the less anisotropic YBaCuO, and from the first order melting ocurring in clean samples to the continuous transitions observed in samples with defects.

cond-mat↗