Artificial kagome lattices of Shockley surface states patterned by halogen hydrogen-bonded organic frameworks

Abstract

Artificial electronic kagome lattices may emerge from electronic potential landscapes using customized structures with exotic supersymmetries, benefiting from the confinement of Shockley surface-state electrons on coinage metals, which offers a flexible approach to realizing intriguing quantum phases of matter that are highly desired but scarce in available kagome materials. Here, we devise a general strategy to construct varieties of electronic kagome lattices by utilizing the on-surface synthesis of halogen hydrogen-bonded organic frameworks (XHOFs). As a proof of concept, we demonstrate three XHOFs on Ag(111) and Au(111) surfaces, which correspondingly deliver regular, breathing, and chiral breathing diatomic-kagome lattices with patterned potential landscapes, showing evident topological edge states at the interfaces. The combination of scanning tunnelling microscopy and noncontact atomic force microscopy, complemented by density functional theory and tight-binding calculations, directly substantiates our method as a reliable and effective way to achieve electronic kagome lattices for engineering quantum states.

Chiral Honeycomb Lattices of Nonplanar π-Conjugated Supramolecules with Protected Dirac and Flat Bands

“…Electronically, the present lattice can be viewed as a hybrid of honeycomb and kagome lattices. While this lattice model has been called star lattice or diatomic kagome lattice, ,− we refer to it as honeycomb-kagome lattice to stress its hybrid character. In the two limiting cases of t 0 / t 1 → ∞ and t 0 / t 1 → 0, it corresponds to the pure honeycomb and kagome lattices, respectively (Figure b).…”

“…These Dirac and flat bands are under intensive investigations because of rich topological and/or many-body phenomena, − but most of them are based on naturally grown inorganic materials and thus lack controllability of model parameters. One of the promising methods for extending the research realm is the usage of molecular assembly such as supramolecules − and metal–organic/covalent-organic frameworks, − where 2D electronic lattices are defined by intermolecular networks ,− or localized Schockley surface states coupled through molecular potential barriers. ,, This approach is based on the rational design of molecules and thus can be very flexible and powerful. However, intermolecular coupling is often very weak, and the general strategy for the formation of a molecular-based honeycomb lattice has not been established yet.…”

“…Here, we adopt a nonplanar π-conjugated molecule Trip-Phz (Figure a), a phenazine analog of triptycene, as a building block for fabricating 2D supramolecular assemblies with pristine molecular electronic bands (Figure b). Trip-Phz and related triptycene molecules are characterized by three polyhedral π-conjugated planes that create a rigid paddle-wheel shape with C 3 -symmetry and are known to form honeycomb supramolecular structures owing to their molecular symmetry. − Electronically, the assembled system can be viewed as a hybrid of the honeycomb and kagome lattices. ,− Dirac and flat bands are predicted by a simple tight-binding model, ,, but the validity of such an approach is not clear yet. This is particularly true when 2D molecular lattices are formed on a supporting substrate, which could strongly modify the intrinsic molecular states due to a finite interfacial interaction.…”

Construction of Two-Dimensional Organometallic Coordination Networks with Both Organic Kagome and Semiregular Metal Lattices on Au(111)

“…The local density of states (LDOS) showed that the 2D organometallic coordination network is semiconducting with a bandgap of 2.3 eV. The corresponding band structure showed no obvious flat band near the Fermi energy, which can be attributed to the asymmetry of the Kagome structure caused by the heterogeneous coordination PGI nodes. , …”

“…The corresponding band structure showed no obvious flat band near the Fermi energy, which can be attributed to the asymmetry of the Kagome structure caused by the heterogeneous coordination PGI nodes. 63,64 Furthermore, we analyzed the charge density difference between the organic ligands and Au adatoms on Au(111). Compared with the 1D metal−organic coordination chain with IGI nodes, a significant amount of charge was redistributed in the 2D organometallic coordination network with PGI nodes (Figure 3e).…”