Triplet dynamics in the VBC-phase of the crossed-chain quantum magnet

Using a series expansion based on the flow-equation method we study the elementary triplet excitations of the frustrated two-dimensional crossed-chain quantum magnet. We show that a region of non-vanishing spin gap exists in the vicinity of the checkerboard point at which the triplets display a frustration-induced localization. Off the checkerboard point a finite triplet dispersion is found and the critical couplings for triplet softening are determined.