Dissipative stabilization and nonlinear saturation of unstable modes

Determine whether the combined action of Gilbert damping and dissipative spin-transfer torques stabilizes negative-energy spin-wave modes in the antiferromagnetic magnonic black-white-hole crystal, and characterize the nonlinear saturation of any unstable modes.

Background

The analysis is conducted in the conservative limit, while realistic insulating antiferromagnets such as MnPSe₃ exhibit weak intrinsic Gilbert damping. The paper argues that damping should primarily produce finite magnon lifetimes without qualitatively changing the band structure or topological phase, but it also notes that positive- and negative-norm mode mixing may generate dynamical instabilities.

Related work in ferromagnetic systems has shown that Gilbert damping combined with dissipative spin-transfer torques can stabilize negative-energy spin-wave modes. It remains unresolved whether an analogous stabilization mechanism applies to the antiferromagnetic crystal studied here. The authors also leave unresolved how nonlinear effects would saturate modes that become unstable.