Two-Dimensionality of Magnetic Excitations on the Trellis Lattice: (La,Sr,Ca)₁₄Cu₂₄O₄₁ and SrCu₂O₃

We explore the properties of magnetic excitations on the trellis lattice which is relevant for the so-called telephone-number compounds A$_{14}$Cu$_{24}$O$_{41}$ and the system SrCu$_2$O$_3$. The trellis lattice consists of two-leg ladders which are coupled in a strongly frustrated fashion. We use the effective model obtained for a single two-leg spin ladder to calculate the two-dimensional one-triplon dispersion and the corresponding one-triplon contribution to the dynamical structure factor. Special attention is laid on signatures of the frustrating inter-ladder magnetic exchange. A detailed suggestion is made for an experimental detection of this exchange in inelastic neutron scattering experiments.