Hole migration in the spin-ladder, dimer chain material Sr2.5Ca11.5Cu24O41

The structure of the (SrxCa1−x)14Cu24O41 series contains both Cu2O3 spin-ladder layers and CuO2 spin chains. Previous measurements on the undoped sample (x=1) showed all the holes were located on the chains, with the magnetic Cu2+ ions on the chain forming a well-defined dimer configuration. We have performed inelastic neutron scattering on a single crystal of the Ca-doped sample Sr2.5Ca11.5Cu24O41. The results show that two magnetic states now coexist on the chain, with one hole per formula unit migrating to the ladders.