Orbital Angular Momentum of Magnons

We study the orbital angular momentum (OAM) of magnons for collinear ferromagnet (FM) and antiferromagnetic (AF) systems with nontrivial networks of exchange interactions [1,2]. The OAM L_zn(k) of magnons at wavevector k and magnon band n for AF and FM zig-zag and honeycomb lattices becomes nonzero when the lattice contains two inequivalent sites and is largest at the avoided-crossing points or extremum of the frequency bands. Hence, the arrangement of exchange interactions may play a more important role at producing the orbital angular momentum of magnons than the spin-orbit coupling energy and the resulting non-collinear arrangement of spins. However, the spin-orbit induced Dzyalloshinskii-Moriya interactions between next-nearest neighbor sites dramatically change our results for the FM honeycomb lattice by producing a nonzero average value <L_zn(k)> for the OAM within each band n = 1 or 2.



References



[1.] R.S. Fishman, J.S. Gardner, and S. Okamoto, Phys. Rev. Lett. 129, 167202 (2022)

[2.] R.S. Fishman, L. Lindsay, and S. Okamoto, J. Phys: Cond. Mat. (in press).