Growth of Mesoscale Ordered Two-Dimensional Hydrogen-Bond Organic Framework with the Observation of Flat Band

Flat bands (FBs), presenting a strongly interacting quantum system, have drawn increasing interest recently. However, experimental growth and synthesis of FB materials have been challenging and have remained elusive for the ideal form of monolayer materials where the FB arises from destructive quantum interference as predicted in 2D lattice models. Here, we report surface growth of a self-assembled monolayer of 2D hydrogen-bond (H-bond) organic frameworks (HOFs) of 1,3,5-tris(4-hydroxyphenyl) benzene (THPB) on Au(111) substrate and the observation of FB. High-resolution scanning tunneling microscopy or spectroscopy shows mesoscale, highly ordered, and uniform THPB HOF domains, while angle-resolved photoemission spectroscopy highlights a FB over the whole Brillouin zone. Densityfunctional-theory calculations and analyses reveal that the observed topological FB arises from a hidden electronic breathing-kagome lattice without atomically breathing bonds. Our findings demonstrate that self-assembly of HOFs provides a viable approach for synthesis of 2D organic topological materials, paving the way to explore many-body quantum states of topological FBs.

Automated summary

In this study, we report the surface growth of a self-assembled monolayer of 2D hydrogen-bond organic frameworks (HOFs) on an Au(111) substrate and the observation of flat bands (FBs). The highly ordered THPB HOF domains and the FB over the whole Brillouin zone were observed through high-resolution scanning tunneling microscopy or spectroscopy and angle-resolved photoemission spectroscopy, respectively. Density functional theory calculations and analyses showed that the observed FB arises from a hidden electronic breathing-kagome lattice without atomically breathing bonds.