Topological spin waves in the atomic-scale magnetic skyrmion crystal

Abstract

We study the spin waves of the triangular skyrmion crystal that emerges in a two-dimensional spin lattice model as a result of the competition between Heisenberg exchange, Dzyalonshinkii-Moriya interactions, Zeeman coupling and uniaxial anisotropy. The calculated spin wave bands have a finite Berry curvature that, in some cases, leads to non-zero Chern numbers, making this system topologically distinct from conventional magnonic systems. We compute the edge spin-waves, expected from the bulk-boundary correspondence principle, and show that they are chiral, which makes them immune to elastic backscattering. Our results illustrate how topological phases can occur in self-generated emergent superlattices at the mesoscale.

Spin-resolved inelastic electron scattering by spin waves in noncollinear magnets

“…[26], which was used to describe a magnetic skyrmion lattice on a hexagonal monolayer. The lattice constant is taken as the unit of length (a = 1).…”

“…We chose J = 1, D = J , B = 0.36 J , and K = 0.25 J as in Ref. [26]. The direction of the Dzyaloshinskii-Moriya vector isn ij =ẑ ×r ij .…”

“…Concurrently, spin waves have been explored for their potential application in spintronic and magnonic devices [15][16][17][18][19]. However, the behavior of spin waves in these noncollinear systems is only now beginning to be understood [20][21][22][23][24][25][26][27][28][29][30].…”

“…To explore this question we need to understand the manifestation of spin waves in these novel magnetic phases: how they may be excited, controlled, and detected. Noncollinear magnetic structures intrinsically feature many spin-wave bands (or modes) due to the breaking of translational and rotational symmetries [26,31]. However, only a few of them can be excited or detected by a given experimental setup.…”

Weyl and Nodal Ring Magnons in Three-Dimensional Honeycomb Lattices

“…Based on these studies, Ezawa [23] proposed a wide class of 3D honeycomb lattices constructed by two building blocks. These 3D honeycomb lattices can display all loop-nodal semimetals which can be gapped to be strong topological insulators by SOI or point nodal semimetals by SOI together with an antiferromagnetic order.Recently, the topology of band has been extended to magnetic excitations as well [24][25][26][27][28][29][30][31][32][33], including magnon Chern insulators [24][25][26][27][28][29], Weyl magnons [30,31], magnon nodal-line semimetals [32] and Dirac magnons [33]. Interestingly, the magnon excitations on a 2D honeycomb lattice with a ferromagnetic ground state have two Dirac points in the first Brillouin zone [28], and a proper DM interaction can gap the system into a magnon Chern insulator, reminiscent of the role of SOI in the graphene [1,2].…”