Phase transitions in and out of equilibrium - order and disorder

The research in my group can be essentially divided into two different directions: phase transitions in and out of equilibrium. In this talk, we will give two examples of our recent work on the two directions, respectively. For equilibrium phase transitions, I will talk about our recent work on melting of 2D polydisperse hard-sphere systems, i.e., hard disks. We find that the particle size polydispersity produces two unexpected effects on the phase behaviour of hard-disk systems: i) polydispersity can dramatically enlarge the packing fraction for stable hexatic phases by one order of magnitude compared to that in systems of monodisperse hard disks; ii) polydispersity can also induced a re-entrant melting of hexatic/crystal phases with increasing density, which has been proven impossible in 3D hard-sphere systems. Therefore, this suggest a fundamental difference in the phase behaviour between polydisperse 2D hard-disk and 3D hard-spheres systems. In the second part of my talk, I will talk about our recent work on circle active particles, in which we find that the non-equilibrium active circle dynamics can drive the system to form a new type of strong hyperuniform fluids with tunable local giant fluctuations. This suggests new possibilities of designing novel active colloids for assembly of dynamic amorphous hierarchical materials.