Twist engineering represents a novel approach to manipulating the magnetic properties of two-dimensional (2D) van der Waals magnets. This technique not only reveals distinctive magnetic structures, including nanoscale magnetic domain arrays but also has the potential to generate magnetic skyrmions—a phenomenon that holds the promise of advancing information technologies. These exciting possibilities have sparked a notable surge of interest in this rapidly growing research domain.

In a recent publication in Nano Letters, a collaborative team led by Dr. KIM Kyoung-Min from the Center for Theoretical Physics of Complex Systems at the Institute for Basic Science in the Republic of Korea, along with Prof. PARK Moon Jip from Hanyang University and Prof. HAN Myung Joon from the Korea Advanced Institute for Science and Technology, achieved significant breakthroughs in the field of twist engineering in 2D van der Waals magnets.

The team's theoretical study delved into the transformation of magnonic band structures under the influence of twists within magnetic systems, with a specific focus on twist bilayer chromium triiodides. In a pioneering revelation, the authors unveiled the emergence of topological magnonic bands and their phase transitions occurring alongside magnetic structural changes.

Their investigations unveiled an intriguing correlation: the topological band structures of magnons are intricately linked to the underlying magnetic structure as illustrated in Figure 1. The magnetic structure undergoes phase transitions as the twist angle is adjusted. Remarkably, the team showcased the realization of two distinct forms of topological magnonic bands within twisted magnets depending on the magnetic structure. These bands each exhibit unique topological edge modes: the “domain-wall boundary mode,” localized alongside the domain-wall boundary, and the “corner magnon mode,” with a localized wave function situated at the system's corner.

This illuminating discovery enhances our understanding of the intricate nature of magnonic band topology within twisted 2D magnets. The study suggests an unprecedented level of controllability over band topology, in stark contrast to the control achieved with topological electronic materials. This insight provides not only a deeper understanding of band topology within magnetic systems but also presents the tantalizing prospect of leveraging twist engineering for tailoring unique topological moiré magnons—an innovative exploration in the realm of fundamental physics as well as materials science and engineering.

Figure 1. Illustration of topological phase transitions in magnonic bands (second row), in conjunction with magnetic phase transitions (first row) during adjustments to the twist angle. Two distinct topological magnonic bands emerge, each characterized by specific topological edge modes: the "domain-wall boundary mode," which displays a localized wave function adjacent to the domain-wall boundary, and the "corner magnon mode," featuring a localized wave function situated at the system's corner.