John Carlos Baez on Nostr: In clean samples of blue bronze, the phasons can travel faster than sound - indeed, ...

In clean samples of blue bronze, the phasons can travel faster than sound - indeed, this is the most famous example of a supersonic lattice excitation. It's possible because the restoring force for the sliding mode of charge density waves has nothing to do with the ordinary stiffness of the crystal.

So: confine some electrons to one-dimensional chains, cool the result down, and they organize themselves into a rippling wave whose collective motions can outrun sound!

But as we cool blue bronze still further, the density waves lock into step with the underlying atomic lattice, and all these effects go away.

(6/n, n = 6)