Probing Dirac excitations in the quantum materials PtTe₂ and PdTe₂ through Angle-Resolved Photoemission Spectroscopy (ARPES)

Low energy excitations in Dirac semimetals, such as Platinum ditelluride (PtTe₂) and palladium ditelluride (PdTe₂), are known to follow a massless Dirac Hamiltonian. In particular, they host type-II excitations that result from a tilt of the three-dimensional Dirac dispersion along the kz direction, which breaks the electron-hole symmetry and violates Lorentz invariance. Such tilted conical energy-momenta dispersion can be probed through ARPES. In addition to type-II Dirac fermions, PtTe₂ and PdTe₂ host topologically protected surface states. Here, we present a detailed study of these different Dirac excitations using both Density Functional Theory (DFT) Calculations and ARPES with different light polarizations. We find signatures both through ARPES and DFT of the different symmetries of the crystallographic space group of these materials that determine their electronic structure. Most importantly, our ARPES data puts in evidence the different nature of the Dirac dispersions that derive from such symmetries: one, a four-fold degenerate cone with no topological protection and the other, a topologically protected non-degenerate cone with chiral states. Additionally, we show preliminary data on a similar quantum material, EuCd₂As₂, identified in literature as a Weyl semimetal.