Designing Intrinsic Topological Insulators in Two-Dimensional Metal-Organic Frameworks.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Chemistry

Background:

• Rational design of metal-organic frameworks (MOFs) relies on understanding the link between their electronic structures and constituent subunits.
• While some 2D conjugated MOFs exhibit topological insulator properties, many lack intrinsic behavior due to Fermi levels misaligned with topological gaps.
• Establishing subunit-to-MOF electronic orbital correspondence is crucial for designing intrinsic topological insulators.

Purpose of the Study:

• To reveal the fundamental role of subunit-to-MOF symmetry in determining electronic orbital interactions and hybridization.
• To understand the design rules for achieving intrinsic metal-organic topological insulators.
• To explore the potential for band structure modulation in honeycomb-kagome MOFs.

Main Methods:

• Analysis of electronic orbital correspondence between MOF subunits and the overall framework.
• Investigation of symmetry relations governing orbital interactions and hybridization.
• Theoretical exploration of electronic band structures in specific MOF architectures.

Main Results:

• Demonstrated that subunit-to-MOF symmetry is fundamental to topological characteristics.
• Identified honeycomb-kagome MOFs with delocalized, symmetry-enforced nonbonding electronic states.
• Observed a topological spin-orbit gap associated with these nonbonding states.

Conclusions:

• The nonbonding nature of these electronic states allows for band structure modulation via molecular structure and strain engineering.
• This work provides a pathway toward the realization of intrinsic metal-organic topological insulators.
• Symmetry-guided design principles are key for developing novel topological materials.