General Stacking Theory for Altermagnetism in Bilayer Systems

TL;DR

This paper introduces a general stacking theory (GST) that predicts the emergence of altermagnetism in bilayer systems based on layer group symmetries, expanding understanding and design possibilities for 2D altermagnetic materials.

Contribution

The paper develops a comprehensive stacking theory (GST) that identifies conditions for altermagnetism in bilayers using symmetry criteria, including cases beyond twisted antiferromagnetic stacks.

Findings

GST predicts altermagnetism in seven specific point groups.

Altermagnetism can occur in symmetrically restricted direct stacking, not just twisted structures.

First-principles calculations confirm the theoretical predictions.

Abstract

Two-dimensional (2D) altermagnetism was recently proposed to be attainable in twisted antiferromagnetic bilayers providing an experimentally feasible approach to realize it in 2D materials. Nevertheless, a comprehensive understanding of the mechanism governing the appearance of altermagnetism in bilayer systems is still absent. In present letter, we address this gap by introducing a general stacking theory (GST) as a key condition for the emergence of altermagnetism in bilayer systems. The GST provides straightforward criteria to predict whether a bilayer demonstrates altermagnetic spin splitting, solely based on the layer groups of the composing monolayers. According to the GST, only seven point groups of bilayers facilitate the emergence of altermagnetism. It is revealed that, beyond the previously proposed antiferromagnetic twisted vdW stacking, altermagnetism can even emerge in bilayers formed through the symmetrically restricted direct stacking of two monolayers. By combining the GST and first-principles calculations, we present illustrative examples of bilayers demonstrating altermagnetism. Our work establishes a robust framework for designing diverse bilayer systems with altermagnetism, thereby opening up new avenues for both fundamental research and practical applications in this field.