In 2013 heavy-fermion uranium (URu2Si2) was cooled to nearly absolute zero, and it produced unexplained heat, then when cooled the particles were arranged in a way that hints hastatic order: the breaking double "time-reversal" symmetry.
This stuff makes my head hurt, I read a bit on it, and don't fully get it.
- T-symmetry is the idea that physics is the same whether time goes forwards or backwards
- Double T-symmetry is the idea that if you reverse time and then reverse it again, everything should end the same.
So what happens is magnetism breaks T-symmetry, but not double T-symmetry. While this stuff breaks that. Though in some bizarre theory Quad-T would restore it, because of Spinors. Yeah, you're getting beyond me.
Basically, URu2Si2 has the weird magnetic property that, below a certain temperature, its response depends severely on the orientation of the field which you apply to it. Which shouldn't really happen by our normal understanding but does. And there's an explanation for how it happens. But is still pretty new, and not fully understood.