arXiv subjects

Giancarlo Ruocco

Publications and source records attributed to Giancarlo Ruocco.

94 records · Page 6Linked to original sources

arXiv2003

Is the Fragility of a Liquid Embedded in the Properties of its Glass?

When a liquid is cooled below its melting temperature it usually crystallizes. However, if the quenching rate is fast enough, it is possible that the system remains in a disordered state, progressively losing its fluidity upon further cooling. When the time needed for the rearrangement of the local atomic structure reaches approximately 100 seconds, the system becomes "solid" for any practical purpose, and this defines the glass transition temperature $T_g$. Approaching this transition from the liquid side, different systems show qualitatively different temperature dependencies of the viscosity, and, accordingly, they have been classified introducing the concept of "fragility". We report experimental observations that relate the microscopic properties of the {\it glassy phase} to the fragility. We find that the vibrational properties of the glass {\it well below} $T_g$ are correlated with the fragility value. Consequently, we extend the fragility concept to the glassy state and indicate how to determine the fragility uniquely from glass properties well below $T_g$.

cond-mat.dis-nn↗

arXiv2001

Quenches and crunchs: Does the system explore in aging the same part of the configuration space explored in equilibrium ?

Numerical studies are providing novel information on the physical processes associated to physical aging. The process of aging has been shown to consist in a slow process of explorations of deeper and deeper minima of the system potential energy surface. In this article we compare the properties of the basins explored in equilibrium with those explored during the aging process both for sudden temperature changes and for sudden density changes. We find that the hypothesis that during the aging process the system explores the part of the configuration space explored in equilibrium holds only for shallow quenches or for the early aging dynamics. At longer times, systematic deviations are observed. In the case of crunches, such deviations are much more apparent.

cond-mat.soft↗

arXiv2000

Observation of Umklapp processes in non-crystalline materials

Umklapp processes are known to exist in cristalline materials, where they control important properties such as thermal conductivity, heat capacity and electrical conductivity. In this work we report the provocative observation of Umklapp processes in a non-periodical system, namely liquid Lithium. The lack of a well defined periodicity seems then not to prevent the existence of these scattering processes mechanisms provided that the local order of the systems i.e. the maxima of the static structure factor supply the equivalent of a reciprocal lattice vector in the case of cristalline materials.

cond-mat.dis-nn↗

arXiv1998

Connected Network of Minima as a Model Glass: Long Time Dynamics

A simple model to investigate the long time dynamics of glass-formers is presented and applied to study a Lennard-Jones system in supercooled and glassy phases. According to our model, the point representing the system in the configurational phase space performs harmonic vibrations around (and activated jumps between) minima pertaining to a connected network. Exploiting the model, in agreement with the experimental results, we find evidence for: i) stretched relaxational dynamics; ii) a strong T-dependence of the stretching parameter; iii) breakdown of the Stokes-Einstein law.

cond-mat.dis-nn↗