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arXiv · 2107.11372

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

Allen Scheie·Pontus Laurell·Paul A. McClarty·Garrett E. Granroth·Matt B. Stone·Roderich Moessner·Stephen E. Nagler
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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.

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Allen Scheie, Pontus Laurell, Paul A. McClarty, Garrett E. Granroth, Matt B. Stone, Roderich Moessner, Stephen E. Nagler. 2021-11-29. Dirac magnons, nodal lines, and nodal plane in elemental gadolinium. https://doi.org/10.1103/physrevlett.128.097201

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