Point-gap topology of damped magnon excitations in skyrmion strings

@misc{koyama2026pointgap,
  title = {{Point-gap topology of damped magnon excitations in skyrmion strings}},
  author = {Yusuke Koyama and Yuki Kawaguchi},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2605.07435},
  eprint = {2605.07435},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2605.07435},
}

TY  - UNPB
TI  - Point-gap topology of damped magnon excitations in skyrmion strings
AU  - Yusuke Koyama
AU  - Yuki Kawaguchi
PY  - 2026
DA  - 2026/10/27
PB  - arXiv
DO  - 10.48550/arxiv.2605.07435
UR  - https://arxiv.org/abs/2605.07435
AB  - We theoretically study the non-Hermitian topology of magnons with finite lifetimes due to Gilbert damping. By incorporating the spin-wave theory and perturbation theory for the Landau-Lifshitz-Gilbert equation including nonlocal damping terms, we analytically evaluate the spectral winding number for point gaps, which indicates the existence of the non-Hermitian skin effect (NHSE). We find that, in noncollinear magnetic textures, the NHSE can occur even in the absence of nonlocal damping, due to the momentum-dependent mixing of the particle and hole components of magnon eigenmodes, which is absent in collinear magnets with a single magnon band. In the presence of nonlocal damping along one direction, we show that the winding number for an energy band with a unique minimum is determined from the sign of the wave number at the band minimum. We demonstrate these results using a model that hosts a skyrmion-string lattice as a steady state. We further investigate spin-wave propagation dynamics excited by a magnetic-field pulse and show that the propagation direction changes drastically from band to band depending on the presence of local and nonlocal damping, consistent with the nontrivial winding numbers.
ER  -