We argue that since the definition of the dielectric function ϵ of a system holds at any coupling strength, and also in the absence of quasi-particles, holographic duality is an ideal framework for computing the dielectric function for strongly correlated systems.
The collective plasmon mode is a self-sustained oscillation driven by the dynamical polarization of the system, which is encoded in the dielectric function. The plasmon mode is obtained as one of the solutions to the vanishing of the dielectric function, and we show that this condition can be solved in holographic duality by a judicious choice of field configuration at spatial infinity. As an example, we study the Reissner-Nordst\"om (RN) metal, dual to the RN black hole, and obtain a gapped plasmon dispersion as expected.
Since the new technique of momentum-resolved electron energy-loss spectroscopy (M-EELS) can be used to measure the dynamical charge response of strange metals, plasmon properties offers a way to compare holographic models to experiments.