Multiple topological phases of magnons induced by Dzyaloshinskii-Moriya and pseudodipolar anisotropic exchange interactions in Kagome ferromagnets

TL;DR

This work addresses topological magnons in a 2D Kagome ferromagnet with multiple anisotropic exchanges, notably Dzyaloshinskii-Moriya (DMI) and pseudo-dipolar (PDI) interactions. Using a linear Holstein-Primakoff approach and paraunitary diagonalization, the authors compute magnon bands, Berry curvatures, and Chern numbers, revealing distinct topological phase diagrams for DMI and PDI and rich high-Chern-number phases when both are present. They show that band inversions and gap closings drive multiple topological transitions and that Berry curvature distributions encode the corresponding Chern-number patterns; they also demonstrate temperature-induced sign reversals of the magnonic thermal Hall and Nernst conductivities with a topological origin. The study highlights the tunability of topological magnons in Kagome magnets via multiple anisotropic interactions, with potential implications for magnonic devices and quantum information processing in materials featuring strong spin-orbit coupling and orbital physics.

Abstract

Kagome magnets naturally hosting Dirac points and flat bands exhibit novel topological phases, enabling rich interplays between interactions and topologies. The discovery of two-dimensional (2D) magnets generally coexisting with different types of magnetic interactions poses a challenge for topological magnonic manipulation. Here we investigate the topological magnon phases of 2D Kagome ferromagnet with multiple magnetic anisotropic interactions, i.e. Dzyaloshinskii-Moriya interaction (DMI) and pseudo-dipolar interaction (PDI). It is found that the different sole magnetic anisotropic interactions introduce completely distinct topological phase diagrams and topological states. The multiple topological magnon phases with high Chern number emerge due to the distinct anisotropic interactions. Moreover, the interplay of the multiple anisotropic DMI and PDI interactions involved with Dirac and flat bands controls a variety of topological phase transitions, implying greater manipulation potential. In addition, the sign reversal of thermal Hall and Nernst conductivities induced by temperature is found in particular topological phase regions, namely topological origin, relating to the energy gap and Berry curvature (Chern number) in the vicinity of magnetic phase transition from the thermal fluctuations, providing a possible explanation for the experimental puzzles. All these results demonstrate that the novel topological magnonic properties in Kagome magnet with multiple magnetic anisotropic interactions can realize a potential platform for magnonic devices and quantum computing.

Figures (13)

• Figure 1: (Color online)(a) The Kagome lattice with three inequivalent atoms with sites 1, 2 and 3, $\mathbf{a_{i}}$ is the lattice vector and $\mathbf{d_{i}}$ is the nearest-neighboring vector. (b) The corresponding Brillouin zone (BZ), and its high-symmetry $\mathbf{k}$-points and $\mathbf{k}$-paths.
• Figure 2: (Color online) $K_{s}$-$F$ phase diagram of classical ground state with fixed parameters $B=0$, $J_{1}$=1, $J_{2}$=0.5 and $D_{z}$=0.2. Insets are the corresponding stable spin configurations.
• Figure 3: (Color online) Band structures of magnons with different parameters (a) $J_{2}$=$D_{z}$=$F$=0, (b) $J_{2}$=0.1 and $D_{z}$=$F$=0, (c) $J_{2}$=$F$=0 and $D_{z}$=0.1, (d)$J_{2}$=$D_{z}$=0 and $F$=5. The Chern numbers $C_{n}$ of each band from top to bottom are marked.
• Figure 4: (Color online) (a) $J_{2}$-$D_{z}$ topological phase diagram. The Chern numbers of the upper (1-st), middle (2-nd) and lower (3-rd) bands are marked in color regions to denote different topological phases. (b) The corresponding minimum band gap $\Delta_{Min}$ between the different magnon bands, i.e. Min($\Delta_{1,2}$, $\Delta_{2,3}$). (c) and (d) are the band gaps between the different magnon bands, $\Delta_{1,2}$ and $\Delta_{2,3}$, for the corresponding topological phase diagram, respectively. Note that the parameter $F=0$ in the absence of PDI.
• Figure 5: (Color online) Enlarged band structures with fixed $D_{z}$=0.2, and $J_{2}$=0.58 (a), 0.59 (b) and 0.6 (c), respectively. The black circles depict the gap closing and opening. The Chern numbers of the corresponding upper, middle and lower bands are marked.