Electron-energy loss spectra and plasmon resonance in cuprates

The consequences of the non-Drude charge response in the normal state of cuprates and the effect of the layered structure on electron-energy loss spectra are investigated, both for experiments in the transmission and the reflection mode. It is shown that in the intermediate doping regime the plasmon resonance has to be nearly critically damped as a result of the anomalous frequency dependence of the relaxation rate. This also implies an unusual low-energy dependence of the loss function. Both facts are consistent with experiments in cuprates. Our study based on the $t-J$ model shows good agreement with measured plasmon frequencies.