Ultra-flat bands at large twist angles in group-V twisted bilayer materials

Area of Science:

• Condensed Matter Physics
• Materials Science
• Computational Physics

Background:

• Flat bands in 2D twisted materials are crucial for observing exotic correlated phenomena.
• Achieving flat bands typically requires large systems and very small twist angles, increasing complexity.
• Group-V elements (P, As, Sb) in the β phase offer a new platform for twisted bilayer materials.

Purpose of the Study:

• To investigate the band structure of group-V twisted bilayer materials (β-P, β-As, β-Sb) with large twist angles.
• To explore the feasibility of achieving ultra-flat bands in these materials, reducing computational and experimental challenges.
• To identify effective methods for tuning the bandgap of flat band systems.

Main Methods:

• Utilized a deep learning method (DeepH) to efficiently calculate the band structure of twisted bilayer materials.
• Simulated twisted bilayer materials containing up to 2524 atoms.
• Investigated the effect of varying twist angles and interlayer distances on band structure properties.

Main Results:

• Demonstrated that bandgap and flat bandwidth decrease with decreasing twist angle in twisted bilayer β-P, β-As, and β-Sb.
• Achieved ultra-flat bands with bandwidths approaching 0 eV.
• Found that a twist angle of 9.43° in β-As yields band flatness comparable to twisted bilayer graphene at its magic angle (1.08°).
• Observed that decreasing interlayer distance reduces the bandgap while preserving the flat band.

Conclusions:

• Group-V twisted bilayer materials provide a feasible platform for realizing and studying flat band phenomena.
• Large twist angles can be effectively used to achieve flat bands, simplifying experimental and computational efforts.
• Interlayer distance is an effective parameter for tuning the bandgap in these flat band systems.