Semiconductor Physics in a 2D Metal: Atomlike Defect States and Anderson Localization in an Air-Stable van der Waals Metal

We have identified a van der Waals (vdW) metal layered metallic crystal that is air-stable and can be exfoliated down to single layers. Angle-resolved photoemission spectroscopy (ARPES) and transport studies provide evidence for S=1 Dirac-Weyl fermions hosted in this novel intermetallic compound. Scanning tunneling spectroscopy on Pd₅AlI₂ reveals two density-of-states resonances above the Fermi level (E_f) that could not be observed in ARPES. Spectroscopic imaging STM (SI-STM) allows the characterization of these states above E_f via quasiparticle interference (QPI). We describe the interpretation of QPI measurements in this compound in terms of the known single-particle band structure from density functional calculations. We proceed to study the effect of lattice defects on this 2D metal. Localized atomlike states are commonly found in semiconductors, but are not usually associated with 3D metals, where screening and hybridization result in extended states within the metallic continuum. Here, we show that Pd₅AlI₂ this material supports strongly localized electronic states that exist within a metallic band – ie, they are an example of bound states in the continuum (BICs). We characterize the wavefunctions and energies of these defect states. Finally, we will describe STM experiments conducted on exfoliated single layers of Pd₅AlI₂ this material and spectroscopic differences between monolayers and the bulk crystal.