Origin of the charge density wave in coupled spin ladders in Sr14-xCaxCu24O41

We formulate a d-p multiband charge transfer model for Cu2O5 coupled spin ladders, relevant for Cu2O3 plane of Sr14-xCaxCu24O41, and solve it using Hartree-Fock approximation. The results explain that (i) the charge density wave (CDW) with its periodicity dependent on doping is stabilized by purely electronic many-body interactions in a single spin ladder and (ii) the inclusion of the interladder interactions favors (disfavors) the stability of the CDW with odd (even) periodicity, respectively. This stays in agreement with recent experimental results and suggests the structure of the minimal microscopic model which should be considered in future more sophisticated studies.