Recent advances of two-dimensional organic topological insulators: surface synthesis and characterization

Two-dimensional (2D) organic topological insulators (OTIs) have garnered increasing interest due to their SOC-induced band gaps and topological boundary states that connect the valence and conduction bands. Experimental efforts utilizing substrate-mediated self-assembly have successfully fabricated 2D organic frameworks with various lattice symmetries. The vast diversity of organic molecules and the wide range of possible coordination interactions between organic ligands and metal atoms have led to significant attention toward these frameworks. However, the experimental realization of large-scale, ordered 2D OTIs remains challenging. In particular, the synthesis of monolayer 2D OTIs featuring nearly flat bands due to destructive quantum interference near the Fermi level has been elusive. With advancements in synthetic chemistry and on-surface synthesis techniques, the number of theoretically-predicted 2D OTIs has been gradually experimentally realized. This review provides a comprehensive summary of recent advances in the synthesis and characterization of 2D OTIs, with a particular focus on the experimental identification of nontrivial flat bands. Finally, we discuss future research directions and the challenges associated with characterizing these novel quantum materials.