Séminaire du LPTMS: Pierre Ronceray & Stefano Spigler *** séminaire exceptionnel ***

1) Stefano Spigler : « Distribution of avalanches in perturbed disordered systems »

Disordered systems under a perturbation usually show a stepwise response, due to the existence of many, sample dependent, local energy minima. In this talk I will show that the distribution of the jumps (static avalanches) of the total energy, under some generic assumptions, depends on the specific system only through its (replica symmetry breaking) order parameter.

2) Pierre Ronceray : « Suppression of crystalline order by competing liquid structures »

Upon cooling, a molecular liquid will eventually either crystallize, or continuously arrest in a amorphous state known as a glass.  What features of the liquid determine this fate? Why is crystallization avoided in glass-formers?  As the liquid is cooled down, the local arrangements of its constituent molecules will increasingly correspond to low-energy configurations.  It is likely that the local structure characterizing the crystalline ground state will be found among these stable arrangements, and one can thus expect that it will accumulate on cooling. However, other non-crystalline structures can also be stable in the liquid, and compete with the accumulation of crystalline order. On what conditions can such a competition stabilize the supercooled liquid to the point of dynamical arrest? We tackle this question using a lattice model where both the crystalline order and the non-crystalline structures are explicitly specified in terms of local configuration of binary spins.  We show that in order to efficiently suppress crystallization, the non-crystalline structure should be energetically and entropically favoured. Importantly, we demonstrate that it must also geometrically antagonize crystalline order. We quantify this effect in terms of overlap of structures: crystal- »agonist » structures with good overlap with the crystal tend to facilitate crystallization, while crystal-antagonist ones tend to impede it and dramatically increase the crystal nucleation time.

 


Date/Time : 16/06/2016 - 11:00 - 12:00

Location : LPTMS, salle 201, 2ème étage, Bât 100, Campus d'Orsay

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