arXiv subjects

Marco Baity-Jesi

Publications and source records attributed to Marco Baity-Jesi.

23 records · Page 2Linked to original sources

arXiv2017

Emergent SO(3) Symmetry of the Frictionless Shear Jamming Transition

We study the shear jamming of athermal frictionless soft spheres, and find that in the thermodynamic limit, a shear-jammed state exists with different elastic properties from the isotropically-jammed state. For example, shear-jammed states can have a non-zero residual shear stress in the thermodynamic limit that arises from long-range stress-stress correlations. As a result, the ratio of the shear and bulk moduli, which in isotropically-jammed systems vanishes as the jamming transition is approached from above, instead approaches a constant. Despite these striking differences, we argue that in a deeper sense, the shear jamming and isotropic jamming transitions actually have the same symmetry, and that the differences can be fully understood by rotating the six-dimensional basis of the elastic modulus tensor.

cond-mat.soft↗

arXiv2016

Criticality and Energy Landscapes in Spin Glasses

Despite the extreme simplicity in their definition, spin glasses disclose a wide variety of non-trivial behaviors that are not yet fully understood. In this thesis we try to shed light on some of them, focusing on one hand on the search of phase transitions under perturbations of the Hamiltonian, and on the other hand on the zero-temperature properties and responses to external stimuli. After introducing spin glasses through a historiographical review, and useful concepts on phase transitions and numerics, the results of two massive Monte Carlo campaigns on three-dimensional systems are shown. In the first one the de Almeida-Thouless transition is studied, and a new finite-size scaling ansatz is proposed, that accelerates the convergence to the thermodynamic limit. In the second one the phase diagram of the Heisenberg spin glass with random exchange anisotropy is reconstructed. In the following part of the manuscript, surprising features of zero-temperature statics and dynamics of several spin glass models are found. Among them, correlations between soft spins that arise spontaneously during avalanches, and the discovery of localized states that involve the presence of two-level systems.

cond-mat.dis-nn↗

arXiv2015

Soft Modes, Localization and Two-Level Systems in Spin Glasses

In the three-dimensional Heisenberg spin glass in a random field we study the properties of the inherent structures that are obtained by an instantaneous cooling from infinite temperature. For not too large field the density of states $g(ω)$ develops localized soft {\em plastic} modes and reaches zero as $ω^4$ (for large fiels a gap appears). When we perturb the system adding a force along the softest mode one reaches very similar minima of the energy, separated by small barriers, that appear to be good candidates for classical two-level systems.

cond-mat.dis-nn↗

arXiv2015

Energy landscape in three-dimensional Heisenberg spin glasses

Recent work suggests that Heisenberg spin glasses may belong to the same universality class than structural glasses. Indeed, finding a lattice equivalent for supercooled liquids would probably allow easier numerical and analytical studies, that may help to answer long-standing questions on the glass transition. Supercooled liquids have many peculiar behaviors that should be found in the paramagnetic phase of Heisenberg spin glasses if the analogy between the two systems holds. It is with this motivation that we undertake a study of the paramagnetic phase of Heisenberg spin glasses. We shall emphasize the role of the energy landscape, with a detailed study of the properties of the inherent structures (by analogy with supercooled liquids, we name inherent structure the local minimum of the energy function which is closest to the current spin configuration). Finding inherent structures will require the development of a new search algorithm. We shall investigate as well the existence of a dynamic transition in the paramagnetic phase. As a matter of fact, both the existence of a complex energy landscape, as well as the existence of a dynamic transition, are distinguished features of the Physics of supercooled liquids.

cond-mat.dis-nn↗

arXiv2015

Dynamics and Correlations among Soft Excitations in Marginally Stable Glasses

Marginal stability is the notion that stability is achieved, but only barely so. This property constrains the ensemble of configurations explored at low temperature in a variety of systems, including spin, electron and structural glasses. A key feature of marginal states is a (saturated) pseudo-gap in the distribution of soft excitations. We study how such a pseudo-gap appears dynamically in the case of the Sherrington-Kirkpatrick (SK) spin glass. After revisiting and correcting the multi-spin-flip criterion for local stability, we show that stationarity along the hysteresis loop requires that soft spins are frustrated among each other, with a correlation that diverges as $C(λ)\sim 1/λ$, where $λ$ is the larger of two considered local fields. We explain how this arises spontaneously in a marginal system and develop an analogy between the spin dynamics in the SK model and random walks in two dimensions. We discuss the applicability of these findings to hard sphere packings.

cond-mat.stat-mech↗