  The band inversion has led to rich physical effects in both topological
insulators and topological semimetals. It has been found that the inverted band
structure with the Mexican-hat dispersion could enhance the interband
correlation leading to a strong intrinsic plasmon excitation. Its frequency
ranges from several $\mathrm{meV}$ to tens of $\mathrm{meV}$ and can be
effectively tuned by the external fields. The electron-hole asymmetric term
splits the peak of the plasmon excitation into double peaks. The fate and
properties of this plasmon excitation can also act as a probe to characterize
the topological phases even in the lightly doped systems. We numerically
demonstrate the impact of the band inversion on plasmon excitations in
magnetically doped thin films of three-dimensional strong topological
insulators, V- or Cr-doped (Bi, Sb)$_2$Te$_3$, which support the quantum
anomalous Hall states. Our work thus sheds some new light on the potential
applications of topological materials in plasmonics.
