Topological Spin Excitations in Honeycomb Ferromagnet CrI3
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In two-dimensional honeycomb ferromagnets, bosonic magnon quasiparticles (spin waves) may either behave as massless Dirac fermions or form topologically protected edge states. The key ingredient defining their nature is the next-nearest-neighbor Dzyaloshinskii-Moriya interaction that breaks the inversion symmetry of the lattice and discriminates chirality of the associated spin-wave excitations. Using inelastic neutron scattering, we find that spin waves of the insulating honeycomb ferromagnet CrI3 (TC=61 K) have two distinctive bands of ferromagnetic excitations separated by a ∼4 meV gap at the Dirac points. These results can only be understood by considering a Heisenberg Hamiltonian with Dzyaloshinskii-Moriya interaction, thus providing experimental evidence that spin waves in CrI3 can have robust topological properties potentially useful for dissipationless spintronic applications.
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Chen, Lebing, Chung, Jae-Ho, Gao, Bin, et al.. "Topological Spin Excitations in Honeycomb Ferromagnet CrI3." Physical Review X, 8, no. 4 (2018) American Physical Society: https://doi.org/10.1103/PhysRevX.8.041028.