Nontrivial topological low-frequency waves at the boundary of magnetized plasmas

The topological properties of a magnetized cold gaseous plasma have recently been explored and the existence of a topologically protected edge states have been established [1,2,3]. These studies are limited to a magnetized plasma, where ions are infinitely massive and provide a neutralizing background. When ion motion is included, a new class of low-frequency unidirectional topological waves emerges in the dispersion relation. The group velocity of these waves is in opposite direction of high frequency topological electron waves for a given magnetic field direction. The Berry curvature and Chern numbers are calculated to establish non-trivial topological phase. A theoretical model is developed for very small inhomogeneity scale lengths to calculate the band-spectrum and establish the existence of an edge mode. It is also presented that if a continuous wave spectrum exists at the boundary of a magnetized plasma, these low-frequency topological waves undergo collisionless damping due to coupling with lower-hybrid resonance, consequently resulting into heating of a plasma. We also demonstrate by ab-initio 3D particle-in-cell simulations that edge states, undergoing collisionless damping, are robust, unidirectional, and topologically protected. These finding broadens the possible applications of these exotic excitations in space and laboratory plasmas.

[1] J. Parker et al, Phys. Rev. Lett. 124, 195001 (2020).

[2] Yichen Fu and Hong Qin, Nature Communications 12, 3924 (2021).

[3] Roopendra S Rajawat, V. Khudik and G. Shvets, arXiv:2203.06693v1(2022)