Dirac magnons, nodal lines, and nodal plane in elemental gadolinium

Abstract

We investigate the magnetic excitations of elemental gadolinium (Gd) using inelastic neutron scattering, showing that Gd is a Dirac magnon material with nodal lines at $K$ and nodal planes at half integer $\ell$. We find an anisotropic intensity winding around the $K$-point Dirac magnon cone, which is interpreted to indicate Berry phase physics. Using linear spin wave theory calculations, we show the nodal lines have non-trivial Berry phases, and topological surface modes. We also discuss the origin of the nodal plane in terms of a screw-axis symmetry, and introduce a topological invariant characterizing its presence and effect on the scattering intensity. Together, these results indicate a highly nontrivial topology, which is generic to hexagonal close packed ferromagnets. We discuss potential implications for other such systems.

4 pages, 4 figures, plus four pages supplemental information. Accompanying paper to arXiv:2107.11370

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• Spin exchange Hamiltonian and topological degeneracies in elemental gadolinium
• Spin Quenching and Transport by Hidden Dzyaloshinskii-Moriya Interactions
• Quantum Geometric Origin of the Intrinsic Nonlinear Hall Effect
• Phonon topology and winding of spectral weight in graphite
• High-throughput search for topological magnon materials
• Pinch points and half moons encode Berry curvature
• Amplifying the antiferromagnetic spin Seebeck effect through topological magnons
• Predicted versatile topological nodal magnons in Tb-based icosahedral quasicrystal 1/1 approximants
• Multiple topological phases of magnons induced by Dzyaloshinskii-Moriya and pseudodipolar anisotropic exchange interactions in Kagome ferromagnets
• Quantum geometry and low-frequency optical conductivity of nodal planes
• Transport of Dirac magnons driven by gauge fields