Many previous posts have discussed the Heisenberg model on the anisotropic triangular lattice which is relevant to the Mott insulating phase in a range of organic charge transfer salts and Cs2CuCl4.
A recent paper suggested that CuNCN is also described by this model, based on DFT based [GGA + U] calculations for the measured crystal structure. They found J1/J2 ~ 0.8 meaning the system could have a spin liquid ground state.
I found this quite exciting.
However, last year some of the same authors suggested a different point of view here, based on a hypothetical crystal structure. I do not follow the arguments in the second paper. Experimentally they do not observe magnetic moments and that motivates looking at alternative crystal structures without antiferromagnetic interactions [at the Hartree-Fock level].
But a non-magnetic ground state is just what you expect for the relevant Heisenberg model in the parameter regime of the first paper.
I think the material and these important questions warrant further study.
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