  We demonstrate how self-sourced collective modes - of which the plasmon is a
prominent example due to its relevance in modern technological applications -
are identified in strongly correlated systems described by holographic Maxwell
theories. The characteristic $\omega \propto \sqrt{k}$ plasmon dispersion for
2D materials, such as graphene, naturally emerges from this formalism. We also
demonstrate this by constructing the first holographic model containing this
feature. This provides new insight into modeling such systems from a
holographic point of view, bottom-up and top-down alike.
  Beyond that, this method provides a general framework to compute the
dynamical charge response of strange metals, which has recently become
experimentally accessible due to the novel technique of momentum-resolved
electron energy-loss spectroscopy (M-EELS). This framework therefore opens up
the exciting possibility of testing holographic models for strange metals
against actual experimental data.
