Quantum magnetic interactions in S=1/2 KCuCl3

KCuCl3 is an S = 1/2 magnetic insulator with a singlet ground state and a f inite spin excitation gap. Above the gap, dispersive tripler excitation mod es propagate in the whole reciprocal space. From single-crystal inelastic n eutron investigations the three-dimensional coupling scheme is rationalized in the framework of a dimer Heisenberg model, and related to the structura l features of KCuCl3. The experimental and theoretical characterization pre sented completes earlier works on the compound under investigation, providi ng also higher-order expressions for the sing]et-triplet dispersion relatio n. The latter may also be of relevance for the parent quantum systems TlCuC l3 and NH4CuCl3, albeit at different coupling ratios with respect to KCuCl3 .