Chlorothionite

While the original mineral Chlorothionite K₂CuSO₄Cl₂ was found in small quantities among the products of volcanic eruption, the synthetic "generalized" crystals of K₂CuSO₄Cl_2-2xBr_2x from our lab definitely capture attention by the size alone. On the scientific side these materials turned out to be an excellent realization of S=1/2 chain model, and continuous substitution of chlorine with bromine changes the exchange constant by almost an order of magnitude. In addition, the simple geometry of this structure allows for a rare kind of perturbation: antisymmetric Dzyaloshinskii-Moriya interaction that is uniform along the chain. Such interaction does substantially modify the quantum dynamics of the spin chain, and these model compounds offer an ideal playground for studying it.