Identifying topological corner states in two-dimensional metal-organic frameworks

Area of Science:

• Condensed Matter Physics
• Materials Science
• Chemistry

Background:

• Two-dimensional (2D) metal-organic frameworks (MOFs) offer diverse molecular building blocks for realizing complex lattice models.
• The study of topological states in materials is crucial for understanding exotic electronic properties.

Purpose of the Study:

• To demonstrate the existence of topological corner states in 2D MOFs with a star lattice configuration.
• To confirm higher-order nontrivial topology in specific energy windows within these MOFs.
• To experimentally identify an organic topological state in a real material.

Main Methods:

• Theoretical demonstration of topological corner states in star lattice 2D MOFs.
• First-principles calculations to investigate electronic band structures.
• Scanning tunneling microscopy (STM) measurements to directly observe topological states.

Main Results:

• Universal existence of topological corner states in star lattice 2D MOFs is demonstrated.
• Higher-order nontrivial topology is confirmed in energy windows between Kagome bands or Dirac and four-bands.
• The first experimental observation of an organic topological state in monolayer Ni3(HITP)2 is achieved.

Conclusions:

• 2D MOFs provide a versatile platform for exploring higher-order topology.
• The experimental identification of organic topological states opens new avenues for topological materials research.
• This work paves the way for studying higher-order topology in 2D MOFs with large band gaps.