Moiré Kramers-Weyl Fermions with Ideal Radial Spin Texture from Structural Chirality

Area of Science:

• Condensed Matter Physics
• Materials Science
• Topological Materials

Background:

• Topological fermions, such as Weyl fermions, exhibit unique electronic properties.
• Spin-orbit coupling and moiré superlattices are key ingredients for engineering novel quantum phenomena.
• Breaking crystal symmetries is crucial for realizing exotic topological states.

Purpose of the Study:

• To theoretically demonstrate the engineering of two-dimensional Kramers-Weyl fermions.
• To investigate the role of symmetry and interlayer coupling in creating these fermions.
• To confirm the experimental realization in specific material systems.

Main Methods:

• Theoretical analysis of spin-orbit coupled twisted bilayers.
• Symmetry analysis under time reversal and C_{nz} symmetry.
• First-principles density functional theory (DFT) calculations.

Main Results:

• Demonstrated the existence of two-dimensional Kramers-Weyl fermions in moiré systems.
• Identified a symmetry-enforced Weyl-like spinful interlayer moiré coupling.
• Confirmed universal ideal radial spin-texture at arbitrary twist angles.
• Realized these fermions in twisted α-In_{2}Se_{3} homobilayers with flat bands and ferroelectric polarization.

Conclusions:

• Two-dimensional Kramers-Weyl fermions can be engineered in specific moiré systems.
• The engineered systems exhibit ideal radial spin textures.
• Twisted α-In_{2}Se_{3} homobilayers provide a promising platform for realizing this novel topological physics.