Conference Presentation (Invited)

FZJ-2025-00007

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Topological magnons in van der Waals ferromagnets CrXTe$_3$ (X = Si, Ge)

Su, Y.FZJ*

2024

Abstract: Recently, two-dimensional van der Waals (2D-vdW) honeycomb ferromagnets have emerged as a new platform for topological spin excitations. In this talk, we present a comprehensive inelastic neutron scattering study and theoretical analysis of the spin-wave excitations in 2D-vdW honeycomb ferromagnets CrXTe3 (X = Si, Ge) [1-2]. Our inelastic neutron scattering experiments show clear dispersive magnonic bands and a well-resolved bandgap opening at the high-symmetry band-crossing Dirac K points in the Brillouin zone. Based on the fitting to experimental data within the linear spin wave theory, the observed bandgap opening was ascribed to the antisymmetric exchange Dzyaloshinskii-Moriya interactions (DMI), and a spin Hamiltonian model including the second nearest-neighbor DMI could provide a very good description of the magnonic dispersion in CrXTe3. The size of the topological magnonic gap was found to be strongly dependent on the strength of the DMI that intrinsically originates from spin-orbit coupling in this system. Furthermore, the Chern numbers of the magnonic bands were found to be nonzero, thus indicating that the bandgap opening is indeed topologically nontrivial and corresponding edge states could emerge inside the gap. On the basis of the compelling evidence obtained in our studies, we thus conclude that the exotic topological magnon insulator, which is intrinsically gap tunable, can be ideally realized in the family of 2D vdW honeycomb ferromagnets CrXTe3. We hope that this discovery will stimulate further investigations on potential technological applications in the domain of magnonics and topological spintronics.[1] Fengfeng Zhu, et al., Sci. Adv. 7, eabi7532 (2021)[2] Li-Chuan Zhang, et al., Phys. Rev. B 103, 134414 (2021)

Keyword(s): Magnetic Materials (1st) ; Information and Communication (1st) ; Magnetism (2nd) ; Condensed Matter Physics (2nd)

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Contributing Institute(s):

1. JCNS-FRM-II (JCNS-FRM-II)
2. Heinz Maier-Leibnitz Zentrum (MLZ)

Research Program(s):

1. 632 - Materials – Quantum, Complex and Functional Materials (POF4-632) (POF4-632)
2. 6G4 - Jülich Centre for Neutron Research (JCNS) (FZJ) (POF4-6G4) (POF4-6G4)

Experiment(s):

1. DNS: Diffuse scattering neutron time of flight spectrometer (NL6S)
2. PUMA: Thermal three axes spectrometer (SR7)
3. ILL-IN12: Cold neutron 3-axis spectrometer
4. Measurement at external facility

Appears in the scientific report 2024

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