SSCU Seminar: Obstructed atomic limit in an in-plane p-orbital decorated Kagome monolayer

Affiliation: Institute for Theoretical Physics and Astrophysics, University of Würzburg, Germany

 Title: “Obstructed atomic limit in an in-plane p-orbital decorated Kagome monolayer”

Electronic bands originating from kagome lattices are known to host a variety of unconventional quantum phenomena, including flat bands, van Hove singularities, and Dirac fermions. In close collaboration with experimental efforts, we present a theoretical investigation of a newly synthesized two-dimensional breathing kagome lattice realized by a monolayer of antimony (Sb) grown on a SiC(0001) substrate. Our analysis demonstrates that substrate-induced orbital filtering suppresses out-of-plane states, leading to an effective low-energy electronic structure dominated by in-plane Sb px and py orbitals. This orbital selectivity gives rise to a characteristic two-orbital kagome band structure near the Fermi level, which is consistently captured by density functional theory and symmetry-based tight-binding modeling, and directly corroborated by angle-resolved photoemission spectroscopy. A substantial electronic gap of approximately 1.77 eV, observed experimentally via scanning tunneling spectroscopy, is attributed to a substrate-engineered breathing distortion of the kagome lattice. From a theoretical band-topological perspective, we identify the resulting gapped phase as an “obstructed atomic insulator”, characterized by nontrivial crystalline topology despite the absence of symmetry-protected gapless boundary states. Motivated by this classification, we perform a systematic theoretical analysis of finite-geometry realizations, focusing on the emergence and robustness of corner-localized modes. Our results reveal a pronounced sensitivity of corner states to the detailed geometric termination, leading to the absence of stable corner-mode localization in experimentally relevant structures. These findings highlight fundamental limitations of bulk–boundary correspondence in two-dimensional systems with crystalline topological invariants and underscore the essential role of geometry in assessing higher-order topological phenomena in realistic materials.