Transition-metal dichalcogenides showing type-II Dirac fermions are emerging as innovative materials for nanoelectronics. However, their excitation spectrum is mostly unexplored yet. By means of high-resolution electron energy loss spectroscopy and density functional theory, here, we identify the collective excitations of type-II Dirac fermions (3D Dirac plasmons) in PtTe_2 single crystals. The observed plasmon energy in the long-wavelength limit is ∼0.5 eV, which makes PtTe_2 suitable for near-infrared optoelectronic applications. We also demonstrate that interband transitions between the two Dirac bands in PtTe_2 give rise to additional excitations at ∼1 and ∼1.4 eV. Our results are crucial to bringing to fruition type-II Dirac semimetals in optoelectronics.
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