We have performed inelastic neutron scattering on a single crystal sample of Sr 14 Cu 24 O 41 to study the spin dynamics of the Cu 2 O 3 spin ladder layers, and CuO 2 chains. Data collected with incident energies of 50 meV, 200 meV, 350 meV and 500 meV are best fitted with a dispersion with a spin gap of 32.5±0.1 meV and a maximum of 193.5±2.4 meV, consistent with a coupling along the ladders, J || = 130 meV and a rung coupling J ⊥ =72 meV. We find that excitations with an energy transfer of approximately 11.5 meV can be described solely in terms of a dimer chain with an antiferromagnetic intra-dimer coupling, J 1 = 11.2 meV, between next-nearest-neighbour Cu ions and a ferromagnetic inter-dimer coupling, J 2 = -1.1 meV. The dimers are separated by two Cu ions providing a periodicity for the dimer chain of five units.

We have performed inelastic neutron scattering on the near ideal spin-ladder compound La4Sr10Cu24O41 as a starting point for investigating doped ladders and their tendency toward superconductivity. A key feature was the separation of one-triplon and two-triplon scattering. Two-triplon scattering is observed quantitatively for the first time and so access is realized to the important strong magnetic quantum fluctuations. The spin gap is found to be 26.4+/-0.3 meV. The data are successfully modeled using the continuous unitary transformation method, and the exchange constants are determined by fitting to be Jleg=186 meV and Jrung=124 meV along the leg and rung, respectively; a substantial cyclic exchange of Jcyc=31 meV is confirmed.

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