Distinct magnetic regimes through site-selective atom substitution in the frustrated quantum antiferromagnet Cs$_2$CuCl$_{4-x}$Br$_x$

A good realization of a spatially anisotropic spin 1/2 triangular lattice is provided by the isostructural layered compounds Cs2CuCl4 and Cs2CuBr4. In this talk, we shall present electronic structure calculations and magnetic susceptibility measurements[1] for the mixed systems Cs$_2$CuCl$_{4-x}$Br$_x$. We shall discuss the existence of three distinct concentration regimes which are separated by critical concentrations x$_{c1}$ = 1 and x$_{c2}$ = 2. The role of frustration effects at the critical concentrations will be highlighted. \\[4pt] [1] Cong et al. Phys. Rev. B 83, 064425 (2011)