Dynamical structure factors of S=1/2 two-leg spin-ladder systems -: art. no. 132415

We investigate the dynamical properties of S=1/2 two-leg spin-ladder systems. In a strong-coupling region, an isolated mode appears in the lowest excited states, while in a weak-coupling region, an isolated mode is reduced and the lowest excited states become a lower bound of the excitation continuum. We find in the system with equal intrachain and interchain couplings that due to a cyclic four-spin interaction, the distribution of the weights for the dynamical structure factor and characteristics of the lowest excited states are strongly influenced. The dynamical properties of the two systems proposed for SrCu2O3 are also discussed.