Miniband Generation by Surface Acoustic Waves.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Acoustics

Background:

• Periodic structures in 2D materials, such as moiré and optical lattices, are crucial for tuning electronic properties.
• Existing methods for creating superlattices have limitations in tunability and amplitude control.
• Surface acoustic waves (SAWs) offer a potential mechanism for dynamic control of material properties.

Purpose of the Study:

• To introduce a novel class of tunable periodic structures using acoustoelectric effects.
• To demonstrate the ability to control the periodicity and amplitude of the superlattice potential.
• To explore the generation of narrow, topologically nontrivial energy bands in 2D materials.

Main Methods:

• Launching two obliquely propagating surface acoustic waves on a piezoelectric substrate supporting a 2D material.
• Utilizing the acoustoelectric effect to create a superlattice potential.
• Employing monolayer graphene as a model system to demonstrate tunability via SAW frequency and power.

Main Results:

• A widely tunable acoustoelectric superlattice was successfully created, with periodicity tunable between moiré and optical lattice scales.
• The amplitude of the acoustoelectric potential was externally controlled by adjusting SAW power, unlike fixed amplitudes in moiré systems.
• In-situ control over the band structure of graphene was achieved, leading to the formation of flat bands and nontrivial valley Chern numbers with localized Berry curvature.

Conclusions:

• The developed acoustoelectric superlattice provides a powerful new platform for engineering the electronic properties of 2D materials.
• External tunability of periodicity and amplitude offers unprecedented control over band structure, enabling the exploration of novel quantum phenomena.
• This technique holds promise for creating designer electronic states and topological devices based on 2D materials.