Dipolar spin-waves and tunable band gap at the Dirac points in the 2D magnet ErBr3

TL;DR

This study reveals how dipolar interactions in 2D ErBr3 create tunable Dirac-like magnon bands and topological gaps, enabling control over magnetic phases and potential applications in topological magnonics.

Contribution

It provides the first experimental and theoretical demonstration of tunable Dirac magnon cones and topological band gaps in a 2D dipolar honeycomb magnet ErBr3.

Findings

Dirac-like magnon cones observed in ErBr3

Band gap opens with dipole rotation, indicating topological transition

Magnetic phases can be reversibly controlled via dipole orientation

Abstract

Topological magnon insulators constitute a growing field of research for their potential use as information carriers without heat dissipation. We report an experimental and theoretical study of the magnetic ground-state and excitations in the van der Waals two-dimensional honeycomb magnet ErBr3. We show that the magnetic properties of this compound are entirely governed by the dipolar interactions which generate a continuously degenerate non-collinear ground-state on the honeycomb lattice with spins confined in the plane. We find that the magnon dispersion exhibits Dirac-like cones when the magnetic moments in the ground-state are related by time-reversal and inversion symmetries associated with a Berry phase \pi as in single-layer graphene. A magnon band gap opens when the dipoles are rotated away from this state, entailing a finite Berry curvature in the vicinity of the K and K' Dirac points. Our results illustrate that the spin-wave dispersion of dipoles on the honeycomb lattice can be reversibly controlled from a magnetic phase with Dirac cones to a topological antiferromagnetic insulator with non-trivial valley Chern number.