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 $χ({\bf q},ω)$ at {\bf Q} = ($π$, $π$) at strong enough inter-site Coulomb repulsion. Together with the strong maximum in the Im $χ({\bf Q},ω)$ 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, $ω_{\bf q}$, along the Brillouin Zone. In particular, we have found that it goes to zero near {\bf Q}$_{CDW} \approx (2π/3, 2π/3)$.