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Chiral Phonons in Moiré Superlattices
Nishchay Suri1, Chong Wang2, Yinhan Zhang1
1Department of Physics, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States.
Nano Letters
|November 16, 2021
Summary
We discovered chiral phonons in moiré superlattices, which are collective excitations arising from stacking configurations. These unique phonons offer new possibilities for phononic twistronics due to their tunability and low energies.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Nanoscience
Background:
- Moiré superlattices exhibit unique electronic and optical properties due to their reduced symmetry and emergent phenomena.
- Phonons, the quantum of lattice vibrations, play a crucial role in material properties and thermal transport.
- Understanding lattice dynamics in moiré systems is essential for exploring novel quantum phenomena.
Purpose of the Study:
- To discover and characterize chiral phonons in the low-energy bands of moiré superlattices.
- To understand the origin and symmetry properties of these novel moiré chiral phonons.
- To provide a general framework for identifying van der Waals heterostructures hosting such phonons.
Main Methods:
- Symmetry analysis within elastic theory to classify van der Waals heterostructures.
- Calculation for twisted molybdenum disulfide (MoS2) as a specific example.
- Development of a low-energy effective model to capture the essential physics of moiré chiral phonons.
Main Results:
- Discovery of chiral phonons originating from stacking domain collective excitations.
- Identification of broken C2 symmetry due to interlayer binding energy as the origin.
- Demonstration of high tunability, moiré-scale wavelengths, and meV-range excitation energies.
Conclusions:
- Moiré chiral phonons are a new class of collective excitations in moiré superlattices.
- The findings provide a complete symmetry classification for hosting these phonons in heterostructures.
- This discovery opens avenues for phononic twistronics with tunable, low-energy excitations.
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