Collective excitations around charge ordered states and coexistent states with different orders

We study qualitative differences of excited states between a charge ordered state and a charge uniform state. The excited states are calculated in the random phase approximation for the one-dimensional extended Hubbard model at quarter Filling. In the charge ordered state, a dominant excitation in t he current-current correlation function has no charge density modulation. A dominant excitation in the charge uniform state originates from crossing t he dimerization gap and modulates the charge density.