This article about time crystals just appeared on the PRL website.
Viewpoint: Crystals of Time (http://physics.aps.org/articles/v5/116)
The authors (including famous Frank Wilczek) claim that some systems in their ground state are time periodic and this is related to some spontaneous breaking of some "time" symmetry. From my point of view such systems were known before this claim (persistent currents, bright solitons among them)...So I want to know what is special about these new "crystals of time"?