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Weyl magnons in breathing pyrochlore antiferromagnets

View Article: PubMed Central - PubMed

ABSTRACT

Frustrated quantum magnets not only provide exotic ground states and unusual magnetic structures, but also support unconventional excitations in many cases. Using a physically relevant spin model for a breathing pyrochlore lattice, we discuss the presence of topological linear band crossings of magnons in antiferromagnets. These are the analogues of Weyl fermions in electronic systems, which we dub Weyl magnons. The bulk Weyl magnon implies the presence of chiral magnon surface states forming arcs at finite energy. We argue that such antiferromagnets present a unique example, in which Weyl points can be manipulated in situ in the laboratory by applied fields. We discuss their appearance specifically in the breathing pyrochlore lattice, and give some general discussion of conditions to find Weyl magnons, and how they may be probed experimentally. Our work may inspire a re-examination of the magnetic excitations in many magnetically ordered systems.

No MeSH data available.


The representative spin-wave spectrum and the Weyl nodes of region I.(a) The spin-wave spectrum along high-symmetry momentum lines with a linear band touching that is marked with a (red) dashed circle. (b) Four Weyl nodes are located at (±k0, 0, 0), (0, ±k0, 0) with k0=1.072π in the xy plane of the Brillouin zone. The (red) circle has an opposite chirality from the (blue) diamond. In the figure, we have set D=0.2J, J′=0.6J and θ=π/2.
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f3: The representative spin-wave spectrum and the Weyl nodes of region I.(a) The spin-wave spectrum along high-symmetry momentum lines with a linear band touching that is marked with a (red) dashed circle. (b) Four Weyl nodes are located at (±k0, 0, 0), (0, ±k0, 0) with k0=1.072π in the xy plane of the Brillouin zone. The (red) circle has an opposite chirality from the (blue) diamond. In the figure, we have set D=0.2J, J′=0.6J and θ=π/2.

Mentions: Regions I and II have the same magnetically ordered structure with the same order parameter and belong to the same phase. Although the ground states are characterized by the same order parameter, the magnetic excitations of the two regions are topologically distinct. The magnetic excitation in region I has Weyl band touchings, while the region II does not. To further clarify this, we choose θ=π/2 and thus fix the magnetic order to orient along the directions of the local coordinate systems. Using linear spin-wave theory, we obtain the magnetic excitation spectrum with respect to this magnetic state for regions I and II. In Fig. 3a, we depict a representative excitation spectrum along the high-symmetry lines in the Brillouin zone for region I.


Weyl magnons in breathing pyrochlore antiferromagnets
The representative spin-wave spectrum and the Weyl nodes of region I.(a) The spin-wave spectrum along high-symmetry momentum lines with a linear band touching that is marked with a (red) dashed circle. (b) Four Weyl nodes are located at (±k0, 0, 0), (0, ±k0, 0) with k0=1.072π in the xy plane of the Brillouin zone. The (red) circle has an opposite chirality from the (blue) diamond. In the figure, we have set D=0.2J, J′=0.6J and θ=π/2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5036007&req=5

f3: The representative spin-wave spectrum and the Weyl nodes of region I.(a) The spin-wave spectrum along high-symmetry momentum lines with a linear band touching that is marked with a (red) dashed circle. (b) Four Weyl nodes are located at (±k0, 0, 0), (0, ±k0, 0) with k0=1.072π in the xy plane of the Brillouin zone. The (red) circle has an opposite chirality from the (blue) diamond. In the figure, we have set D=0.2J, J′=0.6J and θ=π/2.
Mentions: Regions I and II have the same magnetically ordered structure with the same order parameter and belong to the same phase. Although the ground states are characterized by the same order parameter, the magnetic excitations of the two regions are topologically distinct. The magnetic excitation in region I has Weyl band touchings, while the region II does not. To further clarify this, we choose θ=π/2 and thus fix the magnetic order to orient along the directions of the local coordinate systems. Using linear spin-wave theory, we obtain the magnetic excitation spectrum with respect to this magnetic state for regions I and II. In Fig. 3a, we depict a representative excitation spectrum along the high-symmetry lines in the Brillouin zone for region I.

View Article: PubMed Central - PubMed

ABSTRACT

Frustrated quantum magnets not only provide exotic ground states and unusual magnetic structures, but also support unconventional excitations in many cases. Using a physically relevant spin model for a breathing pyrochlore lattice, we discuss the presence of topological linear band crossings of magnons in antiferromagnets. These are the analogues of Weyl fermions in electronic systems, which we dub Weyl magnons. The bulk Weyl magnon implies the presence of chiral magnon surface states forming arcs at finite energy. We argue that such antiferromagnets present a unique example, in which Weyl points can be manipulated in situ in the laboratory by applied fields. We discuss their appearance specifically in the breathing pyrochlore lattice, and give some general discussion of conditions to find Weyl magnons, and how they may be probed experimentally. Our work may inspire a re-examination of the magnetic excitations in many magnetically ordered systems.

No MeSH data available.