We have performed inelastic neutron scattering on the near ideal spin-ladder compound La4Sr10Cu24O41, which will serve as a model system for the investigation of doped ladders. A key feature in the analysis was the separation of one-triplon and two-triplon scattering contributions due to an antiphase rung modulation. This enabled extraction of the one-triplon dispersion which has a spin gap of 26.4+/-0.3 meV, and for the first time two-triplon scattering is clearly observed. The exchange constants are determined by fitting the data to be Jleg=186 meV and Jrung=124 meV along the leg and the rung respectively. In addition to the surprisingly large difference between Jleg and Jrung a substantial ring exchange of Jcyc=31 meV was confirmed.
@article{arxiv.cond-mat/0608109,
title = {One- and Two-Triplon Spectra of a Cuprate Ladder},
author = {S. Notbohm and P. Ribeiro and B. Lake and D. A. Tennant and K. P. Schmidt and G. S. Uhrig and C. Hess and R. Klingeler and G. Behr and B. Buechner and M. Reehuis and R. I. Bewley and C. D. Frost and P. Manuel and R. S. Eccleston},
journal= {arXiv preprint arXiv:cond-mat/0608109},
year = {2009}
}