Hugues Chaté is a Research Director at French Alternative Energies and Atomic Energy Commission (CEA) Paris-Saclay, a Chair Professor at Beijing Computational Science Research Center and the Lead Editor of Physical Review Letters. He obtained his Ph. D. in 1989 from Université Pierre & Marie Curie in Paris. After a short postdoctoral stay at Bell Laboratories, he joined the condensed matter physics department in Saclay. He was the leader of the Advanced Study Group “Statistical Physics of Collective Motion” at the Max Planck Institute for the Physics of Complex Systems in Dresden, Germany. He has been selected as The Recruitment Program of Global Experts, American Physical Society Fellow (2014). Hugues Chaté’s research covers a wide range of topics ranging from nonlinear dynamics to statistical physics and critical phenomena. He has played a seminal role in the development of the field of active matter, with key papers published on minimal models and their theoretical understanding as well as works in collaborations with leading experimentalists working on animal collective behavior, bacteria colonies, and in vitro mixtures of biofilaments and motor proteins. Hugues Chaté has written over 160 scientific papers, with about a third published in Physical Review Letters.

The birth of active matter physics may be traced back to 1995, when Tamas Vicsek and collaborators proposed to see collective motion as a spontaneously broken symmetry phase and introduced the now-famous Vicsek model. The same year, John Toner and Yuhai Tu, inspired by Vicsek, wrote down a field theory for this flying XY spin model, and obtained their landmark result: polar flocks can exhibit true long-range orientational order even in 2D.

Before coming back to these results, the talk will first provide a brief introduction to active matter. Then an account of current knowledge of dry aligning dilute active matter, the relevant case for the Vicsek-Toner-Tu results, will be presented. Next some key facts and issues related to the various instances of long-range order present in this case will be detailed, including recent results showing that true long-range orientational order is also possible in 2D active nematics. If time allows, the robustness of the long-range ordered phases to various types of disorder will be discussed.