General Stacking Theory for Altermagnetism in Bilayer Systems.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Spintronics

Background:

• Two-dimensional (2D) altermagnetism is a novel phenomenon with potential applications in spintronics.
• Previous research suggested twisted antiferromagnetic bilayers as a route to 2D altermagnetism.
• A comprehensive understanding of the underlying mechanisms in bilayer systems was lacking.

Purpose of the Study:

• To develop a theoretical framework for understanding the emergence of altermagnetism in 2D bilayer systems.
• To establish criteria for predicting altermagnetic spin splitting in bilayers.
• To guide the design of new materials exhibiting altermagnetism.

Main Methods:

• Introduction of a General Stacking Theory (GST) based on layer group analysis.
• Theoretical prediction of conditions for altermagnetism in bilayers.
• Validation using first-principles calculations.

Main Results:

• The GST identifies seven specific point groups of bilayers that facilitate altermagnetism.
• Altermagnetism can arise not only from twisted stacking but also from direct stacking of monolayers.
• Illustrative examples of altermagnetic bilayers were computationally demonstrated.

Conclusions:

• The GST provides a robust and general framework for predicting and realizing 2D altermagnetism in diverse bilayer systems.
• This work opens new pathways for fundamental research and technological applications in altermagnetic materials.
• The findings simplify the search for materials with altermagnetic properties.