I will talk about self-propelled organisms (active matter), especially in 2D. Self-propelled directed organisms (Toner and Tu) are found to have an ordered broken-symmetry phase even in 2D, whereas apolar organisms on a substrate display only quasi-long-range order. If I have time I will also talk about some experimental realisations of these systems.
References:
Toner J, Tu Y. 1998. Phys. Rev. E 58:4828–58
Ramaswamy S, Simha RA, Toner J. 2003. Europhys. Lett. 62:196–202
Ramaswamy S. Annu. Rev. Condens.Matter Phys. 2010. 1:323–45
