Ideal topological Weyl complex phonons in two dimensions.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Topology

Background:

• Topological phonons are a recent area of intense research.
• Studies on topological phonons in two-dimensional (2D) systems are scarce.

Purpose of the Study:

• To reveal a novel 2D topological phase involving Weyl phonons.
• To characterize a unique Weyl complex and its symmetry requirements.
• To identify potential material candidates exhibiting this phase.

Main Methods:

• Symmetry analysis to determine the conditions for Weyl complex formation.
• Construction of tight-binding and effective k·p models.
• First-principles calculations for material validation.

Main Results:

• Discovery of a 2D Weyl complex comprising linear and quadratic Weyl nodes.
• Identification of symmetry requirements (rotation, inversion, time-reversal) for the Weyl complex.
• Quantized Berry phases (π and 2π) and emergent chiral symmetry leading to integer topological charges.
• Prediction of unique edge states with three terminals.
• Identification of Cu2Si as a material exhibiting the Weyl complex.

Conclusions:

• This study introduces a novel 2D topological phase with a Weyl complex of topological phonons.
• The findings provide a theoretical framework and symmetry guidance for realizing this phase.
• The identification of Cu2Si validates the theoretical predictions and suggests pathways for experimental verification.