Review of magnons in van der Waals materials: From fundamental physics to frontiers

The magnons (the quanta of collective spin-wave excitations) in two-dimensional van der Waals (vdW) magnets exhibit some intriguing characteristics, such as spin Nernst effect, topological magnons, Weyl magnons, moiré magnons, magnon valley Hall effect, etc., and can be regulated through approaches such as stacking, electric doping, pressure, strain and twisting, opening unprecedented avenues to explore fundamental magnetic physics and spin-based technologies. Over the past few years, intense research efforts have been invested in unraveling magnon properties in vdW materials. This review comprehensively summarizes recent advancements in understanding magnons in vdW magnetic systems, spanning fundamental theories and experimental frontiers. It also introduces the experimental techniques widely used in this field, including inelastic neutron scattering, Raman/Brillouin spectroscopy, time-resolved spectroscopy and inelastic magneto-tunneling spectroscopy, and discusses the coupling between magnons and other excitations, such as phonons and excitons.