Multitude of exceptional points in van der Waals magnets

Several works have recently addressed the emergence of exceptional points (EPs), i.e., degeneracies of non-Hermitian Hamiltonians, in the long-wavelength dynamics of coupled magnetic systems. Here, by focusing on the driven magnetization dynamics of a van der Waals ferromagnetic bilayer, we show that exceptional points can appear over extended portions of the first Brillouin zone as well. Furthermore, we demonstrate that the effective non-Hermitian magnon Hamiltonian, whose eigenvalues are purely real or come in complex conjugate pairs, respects an unusual wavevector-dependent pseudo-Hermiticity. Finally, for both armchair and zigzag nanoribbon geometries, we discuss both the complex and purely real spectra of the topological edge states and their experimental implications.

Automated summary

Several recent works have discussed the emergence of exceptional points in the long-wavelength dynamics of coupled magnetic systems, showing that they can appear over extended portions of the Brillouin zone. The effective non-Hermitian magnon Hamiltonian demonstrates an unusual wavevector-dependent pseudo-Hermiticity, with eigenvalues that are either purely real or in complex conjugate pairs. Additionally, the study discusses the complex and purely real spectra of topological edge states and their experimental implications in both armchair and zigzag nanoribbon geometries.