Observation of the Magnon Hall Effect

Abstract

The Hall effect usually occurs in conductors when the Lorentz force acts on a charge current in the presence of a perpendicular magnetic field. Neutral quasi-particles such as phonons and spins can, however, carry heat current and potentially exhibit the thermal Hall effect without resorting to the Lorentz force. We report experimental evidence for the anomalous thermal Hall effect caused by spin excitations (magnons) in an insulating ferromagnet with a pyrochlore lattice structure. Our theoretical analysis indicates that the propagation of the spin waves is influenced by the Dzyaloshinskii-Moriya spin-orbit interaction, which plays the role of the vector potential, much as in the intrinsic anomalous Hall effect in metallic ferromagnets.

Single-ion anisotropy, Dzyaloshinskii-Moriya interaction, and negative magnetoresistance of the spin-12pyrochloreR2VXiang1, Kan2, Whangbo3 et al. 2011Phys. Rev. B424260View full textAdd to dashboardCite

“…4), which is in agreement with the slight anisotropy displayed in the magnetization curve 10 . If we renormalize the single ion anisotropy term into the DM interaction term, the Hamiltonian is rewritten as:…”

“…Furthermore, Lu 2 V 2 O 7 exhibits a negative magnetoresistance (MR) as high as 50% just above the Curie temperature T C = 73K under magnetic field of 5 T 9 . Recently, Lu 2 V 2 O 7 is found to exhibit a magnon Hall effect (i.e., the anomalous thermal Hall effect caused by spin excitations) 10 . The explanations presented for these observations raise fundamental questions.…”

Emergent functions of quantum materials

“…With a relativistic spin-orbit interaction, this leads to the intrinsic spin Hall effect 66 , the quantized version of which has led to the discovery of topological insulators, described in the next section. Another extension is to consider the Berry phase for neutral particles, such as photons 77,78 and magnons [79][80][81] .…”

Tunable Magnon Weyl Points in Ferromagnetic Pyrochlores

“…Introduction. Ferromagnetic pyrochlores attracted attention with the experimental discovery of the magnon Hall effect [1]: a temperature gradient causes a magnon heat flow in transverse direction. This transverse transport is explained by a Berry curvature in reciprocal space [2][3][4], which is introduced by the Dzyaloshinskii-Moriya (DM) interaction [5,6].…”

“…Moriya's symmetry rules [6] indicate that the DM vectors D i j are perpendicular to the bond that links site i with site j; they are situated at the faces of cubes that enclose tetrahedra [ Fig. 1(b)] [1,15,16].…”