Excitons in nanoribbons derived from a monolayer biphenylene network

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Biphenylene (BPN) is a metallic 2D carbon allotrope, while its boron nitride (BPN-BN) analogue is an insulator.
• This contrast enables in-plane heterostructure engineering for novel electronic properties.

Purpose of the Study:

• To theoretically design and investigate atomically sharp in-plane BPN/BPN-BN heterojunction nanoribbons.
• To explore the impact of edge topology (armchair vs. zigzag) on electronic structure and optical response.
• To understand many-body effects, particularly excitonic phenomena, in these low-dimensional systems.

Main Methods:

• First-principles calculations were employed to study structural stability and electronic properties.
• Systematic investigation of electronic band structure and excitonic optical response.
• Analysis of many-body effects, including exciton binding energies and dielectric screening.

Main Results:

• Edge topology critically dictates electronic behavior: armchair heterojunctions have tunable band gaps (1.3-1.5 eV), while zigzag ones exhibit narrow-gap characteristics.
• Substantial exciton binding energies (>0.20 eV) were observed due to reduced dielectric screening.
• Zigzag heterojunctions show excitonic instability, hinting at excitonic-insulator-like behavior.
• Excitonic effects cause significant red shifts in optical absorption onset.

Conclusions:

• BPN/BPN-BN in-plane heterojunctions offer a versatile platform for edge-controlled band-gap engineering.
• These systems are promising for exploring excitonic physics in nonbenzenoid 2D materials.
• Potential applications in nanoscale optoelectronics and quantum devices are highlighted.