• Zhu, F.; Zhang, L.; Wang, X.; dos Santos, F.J.; Song, J.; Mueller, T.; Schmalzl, K.; Schmidt, W.F.; Ivanov, A.; Park, J.T.; Xu, J.; Ma, J.; Lounis, S.; Blügel, S.; Mokrousov, Y.; Su, Y.; Brückel, T.: Topological magnon insulators in two-dimensional van der Waals ferromagnets CrSiTe3 and CrGeTe3: Toward intrinsic gap-tunability. Science Advances 7 (2021)

Open Access Version

The bosonic analogs of topological insulators have been proposed in numerous theoretical works, but their experimental realization is still very rare, especially for spin systems. Recently, two-dimensional (2D) honeycomb van der Waals ferromagnets have emerged as a new platform for topological spin excitations. Here, via a comprehensive inelastic neutron scattering study and theoretical analysis of the spin-wave excitations, we report the realization of topological magnon insulators in CrXTe3 (X = Si, Ge) compounds. The nontrivial nature and intrinsic tunability of the gap opening at the magnon band-crossing Dirac points are confirmed, while the emergence of the corresponding in-gap topological edge states is demonstrated theoretically. The realization of topological magnon insulators with intrinsic gap-unability in this class of remarkable 2D materials will undoubtedly lead to new and fascinating technological applications in the domain of magnonics and topological spintronics.