Charge density wave in the spin ladder of   Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$
  We consider a multiband charge transfer model for a single spin ladder describing the holes in Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$. Using Hartree-Fock approximation we show how the charge density wave, with its periodicity dependent on doping as recently observed in the experiment, can be stabilized by purely electronic many-body interactions. 
Krzysztof Wohlfeld, Andrzej M. Oles, George A. Sawatzky