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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.

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Surface states of a slab.The slab is cleaved along the [11] surface, setting D=0.2J, J′=0.6J and θ=π/2. (a) Magnon arcs in the surface Brillouin zone. Γ0 is the origin of the Brillouin zone and two reciprocal lattice vectors are , . The surface states with E=EWeyl form arcs connecting the Weyl nodes with different chiralities, where EWeyl is the energy of the bulk Weyl nodes. States along the two pink longer (green shorter) arcs are localized in the top (bottom) surface. (b) The (blue) bulk magnon excitations and the (red) chiral surface states along . The (green) dashed line indicates E=EWeyl.
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f4: Surface states of a slab.The slab is cleaved along the [11] surface, setting D=0.2J, J′=0.6J and θ=π/2. (a) Magnon arcs in the surface Brillouin zone. Γ0 is the origin of the Brillouin zone and two reciprocal lattice vectors are , . The surface states with E=EWeyl form arcs connecting the Weyl nodes with different chiralities, where EWeyl is the energy of the bulk Weyl nodes. States along the two pink longer (green shorter) arcs are localized in the top (bottom) surface. (b) The (blue) bulk magnon excitations and the (red) chiral surface states along . The (green) dashed line indicates E=EWeyl.

Mentions: Due to the bulk-edge correspondence, we expect magnon arc states bound to any surface which possesses non-trivial projections of the bulk Weyl points. This is indeed observed in Fig. 4. The chiral magnon arcs appear at non-zero energy and connect the bulk magnon Weyl nodes with opposite chiralities, as expected.


Weyl magnons in breathing pyrochlore antiferromagnets
Surface states of a slab.The slab is cleaved along the [11] surface, setting D=0.2J, J′=0.6J and θ=π/2. (a) Magnon arcs in the surface Brillouin zone. Γ0 is the origin of the Brillouin zone and two reciprocal lattice vectors are , . The surface states with E=EWeyl form arcs connecting the Weyl nodes with different chiralities, where EWeyl is the energy of the bulk Weyl nodes. States along the two pink longer (green shorter) arcs are localized in the top (bottom) surface. (b) The (blue) bulk magnon excitations and the (red) chiral surface states along . The (green) dashed line indicates E=EWeyl.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f4: Surface states of a slab.The slab is cleaved along the [11] surface, setting D=0.2J, J′=0.6J and θ=π/2. (a) Magnon arcs in the surface Brillouin zone. Γ0 is the origin of the Brillouin zone and two reciprocal lattice vectors are , . The surface states with E=EWeyl form arcs connecting the Weyl nodes with different chiralities, where EWeyl is the energy of the bulk Weyl nodes. States along the two pink longer (green shorter) arcs are localized in the top (bottom) surface. (b) The (blue) bulk magnon excitations and the (red) chiral surface states along . The (green) dashed line indicates E=EWeyl.
Mentions: Due to the bulk-edge correspondence, we expect magnon arc states bound to any surface which possesses non-trivial projections of the bulk Weyl points. This is indeed observed in Fig. 4. The chiral magnon arcs appear at non-zero energy and connect the bulk magnon Weyl nodes with opposite chiralities, as expected.

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.


Related in: MedlinePlus