Wednesday, August 21, 2013

Copper sulphate is a spin liquid

It is amazing since a common science project for school children is to make blue crystals of copper sulphate [CuSO4.5H2O]!
[Although I was surprised and disappointed when my son just told me he never did it].

Perhaps, one may not have to look so hard for quantum materials.

The first X-ray crystallography experiment [by von Laue] was also performed on copper sulphate pentahydrate.

It turns out that the Cu2+ ions (spin-1/2) form chains that are very weakly coupled to one another and so are effectively one-dimensional antiferromagnetic Heisenberg chains above the three-dimensional Neel ordering temperature of about 100 mK.
[Caveat: strictly speaking half of the Cu2+ ions form chains; the other half are essentially isolated and non-interacting].

Minor caveat: the relevant intrachain exchange interaction J ~ 0.25 meV and so one only sees the spinons for temperatures of order a Kelvin.

I first learned all this in the introduction of this Nature Physics paper.


  1. I grow nice crystals of this stuff at home with commercial "Root Kill" from the hardware store.

    Geballe mentions growing a 1400g single crystal for his graduate work in his recent Annual Review article:

  2. I could look at that rock all day, honestly. What a nice colour.