Orbital Engineering Band Degeneracy in a Dual-Square Carbon-Oxide Framework

Area of Science:

• Condensed matter physics
• Materials science
• Quantum phenomena

Background:

• Electron band degeneracies create exotic quantum phenomena.
• Nodal-lines arise from band touching in specific symmetries.
• Synthetic 2D quantum materials from covalent-organic frameworks (COFs) are underexplored.

Purpose of the Study:

• To present a molecular orbital engineering approach for designing 2D quantum materials.
• To fabricate an edge-centered dual square lattice within a π-conjugated 2D-tetraoxa[8]circulene (2D-TOC) COF.
• To explore emergent topological phenomena in synthetic 2D materials.

Main Methods:

• Molecular orbital engineering.
• Fabrication of π-conjugated 2D-TOC COF.
• First-principles calculations.
• Scanning tunnelling spectroscopy.

Main Results:

• Successfully designed and fabricated an edge-centered dual square lattice in 2D-TOC COF.
• Observed Frontier states at the center of a 3 × 3 lattice.
• Revealed the emergence of Dirac nodal-lines in the 2D-TOC material.

Conclusions:

• The study provides a general guide for designing conjugated COFs with tailored electronic properties.
• The findings enable exploration of emergent topological phenomena in synthetic 2D materials.
• The developed 2D-TOC COF has potential applications in high-speed, low-power data processing, transmission, and storage.