2024/09/11 by R. S. Fishman, Fishman, Randy S., Daniel M. Pajerowski +1
Chemical Engineering · Physics and Astronomy · #Advanced Condensed Matter Physics #Catalysis and Oxidation Reactions #FOS: Physical sciences #Materials Science (cond-mat.mtrl-sci) #Theoretical and Computational Physics
paper · pdf · doi:10.48550/arxiv.2409.07319
openalex publication_date 2024/09/11 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We study the Berry curvature and Chern number of a non-collinear spin state on a honeycomb lattice that evolves from coplanar to ferromagnetic with a magnetic field applied along the z axis. The coplanar state is stabilized by nearest-neighbor ferromagnetic interactions, single-ion anisotropy along z, and Dzyalloshinskii-Moriya interactions between next-nearest neighbor sites. Below the critical field Hc that aligns the spins, the magnetic unit cell contains M=6 sites and the spin dynamics contains six magnon subbands. Although the classical energy is degenerate wrt the twist angle ϕ between nearest-neighbor spins, the dependence of the free energy on ϕ at low temperatures is dominated by the magnon zero-point energy, which contains extremum at ϕ=πl/3 for integer l. The only unique ground states GS(ϕ) have l=0 or 1. For H < Hc', the zero-point energy has minima at even l and the ground state is GS(0). For Hc' < H < Hc, the zero-point energy has minima at odd l and the ground state is GS(π/3). In GS(0), the magnon density-of-states exhibits five distinct phases with increasing field associated with the opening and closing of energy gaps between the two or three magnonic bands, each containing between 1 and 4 four magnon subbands. While the Berry curvature vanishes for the coplanar ϕ=0 phase in zero field, the Berry curvature and Chern numbers exhibit signatures of the five phases at nonzero fields below Hc'. If ϕ≠ πl/3, the Chern numbers of the two or three magnonic bands are non-integer. We also evaluate the inelastic neutron-scattering spectrum S(\vk ,ω) produced by the six magnon subbands in all five phases of GS(0) and in GS(π/3).