Quasi-two-dimensional hole ordering and dimerized state in the CuO2-chain layers in Sr14CU24O41

Neutron-scattering experiments have been performed on Sr14Cu24O41 that consists of both chains and ladders of copper ions. We observed that the magnetic excitations from the CuO2 chain have two branches and that both branches are weakly dispersive along the a and c axes. The omega-Q dispersion relation as well as the intensities can be reasonably described by a random-phase approximation with intradimer coupling J = 11 meV, interdimer coupling along the c axis J(c)=0.75 meV, and interdimer coupling along the a axis J(a)=0.75 meV. The dimer configuration indicates a quasi-two-dimensional hole ordering, resulting in an ordering of magnetic Cu2+ With spin-1/2 and nonmagnetic Cu, which forms the Zhang-Rice singlet. We have also studied the effect of Ca substitution for Sr on the dimer and the hole ordering. [S0163-1829(99)11401-2].