Observation of Gapped Topological Surface States and Isolated Surface Resonances in PdTe 2 Ultrathin Films.

The superconductor PdTe ₂ is known to host bulk Dirac bands and topological surface states. The coexistence of superconductivity and topological surface states makes PdTe ₂ a promising platform for exploring topological superconductivity and Majorana bound states. In this work, we report the spectroscopic characterization of ultrathin PdTe ₂ films with thickness down to three monolayers (ML). In the 3 ML PdTe ₂ film, we observed spin-polarized surface resonance states, which are isolated from the bulk bands due to the quantum size effects. In addition, the hybridization of surface states on opposite faces leads to a thickness-dependent gap in the topological surface Dirac bands. Our photoemission results show clearly that the size of the hybridization gap increases as the film thickness is reduced. The observation of isolated surface resonances and gapped topological surface states sheds light on the applications of PdTe ₂ quantum films in spintronics and topological quantum computation.