Twist-induced altermagnetism in a metallic van der Waals antiferromagnet

TL;DR

This study demonstrates that twist engineering in a metallic van der Waals antiferromagnet induces altermagnetism, characterized by spin-polarized bands at zero net magnetization, offering new pathways for 2D spintronic device development.

Contribution

First-principles calculations show twist-induced breaking of PT symmetry in Fe-based bilayer antiferromagnets creates a robust altermagnetic state with significant spin splitting.

Findings

Spin splitting up to 138 meV observed.

PT symmetry broken by twisting layers.

Electronic states show spin degeneracy along high-symmetry directions.

Abstract

Altermagnetism -a magnetic state characterized by spin-polarized electronic bands at zero net magnetization- offers a promising route for next-generation spintronic devices. In two-dimensional (2D) magnets, twist engineering enables its realization by breaking the combined inversion and time-reversal symmetry (PT) while preserving crystal symmetries that ensure the altermagnetic order. Here, by means of first-principles calculations and symmetry analysis, we demonstrate that twist engineering applied to the recently synthesized metallic van der Waals antiferromagnet Co-doped bilayer Fe$_3$GaTe$_2$ (Fe$_2$CoGaTe$_2$) provides a robust platform for altermagnetism. By twisting two layers of Fe$_2$CoGaTe$_2$, the PT symmetry between opposite spin sublattices is broken, resulting in a non-relativistic $i$-wave altermagnetic state with spin splitting up to 138 meV. In the absence of spin-orbit coupling (SOC), the electronic states are spin-degenerate along six high-symmetry directions, while the inclusion of SOC preserves this degeneracy along the three directions protected by twofold rotation axes. Furthermore, we unveil the microscopic mechanisms governing the magnetic behavior in twisted Fe$_2$CoGaTe$_2$. Our results establish twist engineering and metallic Fe-based van der Waals antiferromagnets as versatile platforms to realize 2D van der Waals altermagnetism, with potential for designing high-efficiency ultrathin nanodevices.