Dimensionality-Driven Terahertz Dirac Magnons in Layered 3<i>d</i> Ferromagnets.

Abstract

Harnessing symmetry-protected terahertz Dirac magnons would enable robust, low-loss magnonic transport, offering a compelling alternative to conventional information carriers. Here we propose a novel yet remarkably simple platform for hosting terahertz Dirac magnons in low-dimensional magnetic architectures. We demonstrate, through first-principles calculations and linear spin-wave theory, that atomically designed magnetic layers possessing <i>C</i>_3<i>v</i> symmetry can exhibit Dirac magnon band crossings and a quantized Berry phase of ±π. The formation of the Dirac point, absent in their bulk counterpart, is a direct consequence of the reduced dimensionality. Our finding not only highlights the unique dimensionality-driven Dirac magnons in layered structures but also sheds light on the complex behavior of the Berry phase in such structures. We show that parameters such as surface symmetry, atomic layer composition, film thickness, epitaxial relationship, and chemical environment can be used to tune the Berry phase and the resulting symmetry-associated properties.