Isospin model for suppression of charge order in hole- doped NaV_2O_5
  The layered perovskite compound NaV_2O_5 exhibits charge ordering (CO) and spin gap formation which is driven by inter- site Coulomb forces and exchange dimerisation. Experimentally it was found that the CO transition is rapidly reduced by doping. Charge ordering in NaV_2O_5 has a quasi 1D character due to inter- ladder frustration in the Trellis lattice. Based on an extended pseudospin (T=1) approach for hole doped NaV_2O_5 ladders we construct an Ising like model that explains qualitatively the destruction of the CO phase as function of hole doping \delta and show how the CO parameter depends on \delta and the ratio of Coulomb and hopping energies. 
P. Thalmeier