Broadband excitation spectrum of bulk crystals and thin layers of PtTe2

We explore the broadband excitation spectrum of bulk PtTe2 using electron energy-loss spectroscopy and density-functional theory. In addition to infrared modes related to intraband three-dimensional (3D) Dirac plasmon and interband transitions between the 3D Dirac bands, we observe modes at 3.9, 7.5, and 19.0 eV in the ultraviolet region. The comparison of the excitation spectrum with the calculated orbital-resolved density of states allows us to ascribe spectral features to transitions between specific electronic states. Additionally, we study the thickness dependence of the high-energy-loss peak in the PtTe2 thin films. We show that, unlike graphene, the high-energy EELS peak in PtTe2 thin film gets redshifted by ∼2.5 eV with increasing thickness.