Fecha y Horario:

20 de octubre de 2017, 13hs

Orador:

Leticia Cugliandolo

Afiliación:

Université Pierre et Marie Curie - Paris

Resumen:

Active matter is essentially out of equilibrium. The large number of interacting constituents consume energy from the environment and use it to move, typically in a preferred direction, or to exert mechanical forces.

Most examples of active matter are biological in origin; however, a great deal of current experimental work is devoted to synthetic systems. Of the first kind are schools of fish, flocks of birds and bacteria, of the latter, artificial self-propelled particles are built in various ways.

Active matter exists in three but also in two dimensions and it is often studied, analytically and numerically, on the plane. The first obvious question is which are the out of equilibrium phases that can be sustained under such energy injection.

Melting in two spatial dimensions, as realized in thin films or at interfaces, represents one of the most fascinating phase transitions in nature, but it still remains poorly understood. A new melting scenario was recently exhibited for the hard (and not so soft) passive disk model. In this picture, the hexatic-solid transition is continuous while, surprisingly, the liquid-hexatic transition is of first-order allowing for co-existence between these two phases.

In a recent work we showed co-existence between hexatically ordered and liquid/gas phases over a finite interval of packing fractions in active repulsive dumbbell systems in two dimensions. In the passive limit this interval remains finite, similarly to what has been observed in bidimensional systems of hard and soft disks. This picture is different from the one that was so-far proposed for two-dimensional active matter, that goes under the name of mobility induced phase transition.

I will discuss all these issues in a general way.

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