Dynamical charge susceptibility in layered cuprates: the influence of screened inter-site Coulomb repulsion

Abstract

The analytical expression for dynamical charge susceptibility in layered cuprates has been derived in the frame of singlet-correlated band model beyond random-phase-approximation (RPA) scheme. Our calculations performed near optimal doping regime show that there is a peak in real part of the charge susceptibility $\chi (\mathbf{q},\omega )$ at {\bf Q} = ($\pi$, $\pi$) at strong enough inter-site Coulomb repulsion. Together with the strong maximum in the Im $\chi (\mathbf{Q},\omega )$ at 15 meV it confirms the formation of low-energetic plasmons or charge fluctuations. This provides a jsutification that these excitations are important and together with a spin flcutuations can contribute to the Cooper pairing in layered cuprates. Analysing the charge susceptibilitiy with respect to an instability we obtain a new plasmon branch, ${\omega }_{\mathbf{q}}$, along the Brillouin Zone. In particular, we have found that it goes to zero near {\bf Q}${}_{CDW}\approx (2\pi /3,2\pi /3)$.