Moiré collective vibrations in atomically thin van der Waals superlattices

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Collective vibrations are crucial for material properties like thermal, electrical, and topological characteristics.
• Moiré superlattices offer tunable interfacial structures that can manipulate collective excitations at the atomic scale.

Purpose of the Study:

• To experimentally demonstrate and characterize moiré collective vibrations at the heterointerfaces of twisted tungsten diselenide/tungsten disulfide heterobilayers.
• To investigate the relationship between moiré periodicity, interlayer vibrations, and moiré excitons.

Main Methods:

• Helicity-resolved inelastic Raman scattering was employed to detect and analyze interfacial phonons.
• The study involved mutual torsion of heterobilayers to observe changes in interlayer vibrations.

Main Results:

• Chiral interfacial phonons carrying angular momentum were identified, analogous to chiral bulk phonons.
• Terahertz interlayer vibrations were observed to be proportional to moiré periodicity and tunable with rotation angles.
• A distinct long-lived breathing mode with zero angular momentum and high energy was observed in the low-angle strong coupling regime, indicating phonon hybridization.

Conclusions:

• Moiré collective vibrations, including chiral interfacial phonons and moiré-tuned interlayer modes, were experimentally demonstrated.
• These findings highlight the potential for exploiting moiré collective vibrations in applications such as thermal management, electrical engineering, and topological phononics.