Winding feature and thermal evolution of the Dirac magnons in CrI$_3$

TL;DR

This study reveals the Dirac magnon winding feature and temperature-dependent energy renormalization in CrI$_3$, highlighting its topological magnon properties and magnon-magnon interactions.

Contribution

First experimental observation of Dirac magnon winding and thermal evolution in CrI$_3$, advancing understanding of topological magnons in 2D ferromagnets.

Findings

Magnon winding feature around the K-point identified.

Magnon energy exhibits T^2 renormalization at higher temperatures.

Results support the topological nature of CrI$_3$'s spin excitations.

Abstract

Two-dimensional honeycomb lattice ferromagnet chromium tri-iodide (CrI$_3$) has attracted tremendous interest because it retains ferromagnetism down to the monolayer limit and hosts intriguing topological magnons. As a prototypical van der Waals magnet, CrI$_3$ provides an ideal platform for exploring the interplay between reduced dimensionality, magnetic order, and nontrivial spin excitations. Here, using inelastic neutron scattering together with improved sample quality, we uncover the magnon winding feature around the $K$-point of the hexagonal Brillouin zone, a key signature of Dirac magnons. In addition, we find that the magnon energy follows a $T^2$-renormalization behavior at elevated temperatures, consistent with magnon-magnon interactions. These results provide previously missing information on the magnon spectrum of CrI$_3$ and further consolidate the topological nature of its spin excitations.