CQX  

The family of copper quinoxaline halides is a rare example of the spin ladder materials in which the continuous chemical substituition of chloride with bromide can be carries out without any structural transitions. The exchange constants are clearly changing as the result of it, but not dramatically. Basically, CQX ladders always stay close to the "isotropic" limit with nearly equal leg and rung exchanges. The smallness of crystals and somewhat large energy scale make CQX a difficult target for most experimental techniques, but that is just ideal for Raman scattering. A two-magnon continuum in a ladder can be observed with ease by light scattering, and tracing this continuum as function of composition confirms the continuous nature of exchange constants tuning.