Programmable Higher-Order Topological Phases in Open-Shell Metal-Organic Frameworks.

Area of Science:

• Materials Science
• Chemistry
• Physics

Background:

• Metal-organic frameworks (MOFs) are highly tunable but often lack electronic functionality due to their insulating nature.
• Developing MOFs with tailored electronic properties is crucial for advanced quantum applications.

Purpose of the Study:

• To introduce a general strategy for creating topological MOFs with programmable electronic functionality.
• To leverage open-shell ligands for novel MOF construction.

Main Methods:

• On-surface synthesis of cobalt-coordination networks using radical nanographene linkers.
• Fabrication of Sierpiński-triangle fractal MOFs on Au(111).
• Characterization using low-temperature scanning tunneling microscopy/spectroscopy and tip-induced assembly.

Main Results:

• Emergent electronic states spanning the Fermi level were observed in the synthesized MOFs.
• Topologically protected corner modes, characteristic of higher-order topological phases, were directly detected.
• Systematic tuning of fractal hierarchy and monitoring of topological states were achieved via precise molecular assembly.

Conclusions:

• Open-shell ligand chemistry provides a versatile pathway to topological MOFs.
• This approach enables the design of molecular quantum materials with programmable electronic and quantum properties.
• The findings pave the way for next-generation electronic and quantum devices.