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In a recent paper by Husain et al. [PRX 9, 041062 (2019)], the two-particleelectronic excitations in Bi2Sr2CaCu2O8+x have been studied by ElectronEnergy-Loss Spectroscopy in reflection (R-EELS) in the strange metal rangebetween underdoped and overdoped materials. The authors conclude that there areno well defined plasmons. Rather they obtain a momentum-independent continuumwhich they discuss in terms of holographic theories. In this Comment it ispointed out that the experimental results are in stark contrast to previousEELS in transmission (T-EELS), Resonant Inelastic X-ray Scattering (RIXS), andoptical studies. The differences can be probably explained by an inaccuratemomentum scale in the R-EELS experiments. Furthermore, it is shown, that manymaterial specific experimental results from T-EELS, R-EELS, RIXS, and opticalspectroscopy can be explained by a more traditional extended Lindhard model.This model describes the energy, the width, and the dispersion of normal andacoustic plasmons in cuprates, as well as the continuum. The latter isexplained by electron-hole excitations inside a lifetime broadened conductionband. This continuum is directly related to the scattering rates of the chargecarriers, which in turn, by a feed back process, lead to the continuum.

Comment on: Crossover of Charge Fluctuations across the Strange Metal Phase Diagram