High-energy electronic excitations in a bulk MoS2 single crystal

The collective electronic excitations and their dispersion behavior across both the first and second Brillouin zones in a bulk $\mathrm{Mo}{\mathrm{S}}₂$ single crystal have been investigated using nonresonant inelastic hard x-ray scattering and time-dependent density-functional theory. The experiment results revealed two main plasmons located around 8.6 and 23 eV. The $\ensuremath{\sim}8.6\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ plasmon shows clear anisotropic behavior and was only observed in plane due to the two-dimensional geometry. In addition, theoretical calculation indicates that the dispersion behavior of this in-plane plasmon shows weak momentum dependence. The main plasmon near 23 eV demonstrates an isotropic three-dimensional collective electron excitation behavior, which suggests a weak correlation between the electron excitation and layered lattice structure. This behavior is completely different from the anisotropic dispersion behavior found in layered graphite. Our work provides clear experimental and theoretical data on the dynamic electronic behavior of excited high-energy electrons in $\mathrm{Mo}{\mathrm{S}}₂$, which not only provides guidance on device design but also furthers understanding of electronic behaviors in other similar systems.