Dresden 2026 – scientific programme

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PLV: Plenarvorträge

PV VII

PLV PV VII: Plenary Talk

Wednesday, March 11, 2026, 14:00–14:45, HSZ/0002

Stronger yet weaker: Long-range orientational order in 2D active matter — •Hugues Chaté — CEA - Saclay, France

The Mermin-Wagner-Hohenberg theorem tells us that, in a 2D system in equilibrium, the spontaneous breaking of a continuous symmetry cannot lead to true long-range order. Out of equilibrium, and in particular in active matter systems, it is now well known that 2D true long-range orientational order is possible.

I will first give an updated view of our knowledge of polarly ordered phases in 2D active matter systems. I will then proceed to show that many of these phases are metastable to the nucleation of droplets which, opposite to the Peierls argument at play in equilibrium, grow and eventually destroy order. Order is thus both stronger (truly long-range) and weaker (metastable) in 2D active systems.

Keywords: active matter; long-range order; metastability