Magnon polarons: Hybrid quasiparticles in coupled spin–lattice systems

The concept of hybrid quasiparticles has emerged as a cornerstone of modern condensed matter physics, offering powerful means to control material properties and engineer new functionalities. Among these, the magnon polarons (MPs), a mixed state arising from the strong coupling between magnons (spin wave excitations) and phonons (lattice vibrations), have recently garnered significant attention. This review article comprehensively investigates recent advancements in the field of MPs. We begin by elucidating the fundamental magnetoelastic coupling mechanisms that underlie the formation of MPs. A detailed account of the primary experimental techniques, including inelastic neutron scattering and light scattering, are provided, highlighting their unique roles in probing the spectral and spatial properties of MPs. Furthermore, we explore the profound implications of the formation of MPs on spin and heat transport phenomena, such as the spin pumping, spin Seebeck effect, and spin Peltier effect. We then present a panorama of material systems where MPs have been experimentally observed, ranging from rare-earth iron garnets to antiferromagnets, multiferroic materials, and van der Waals magnets. Finally, we discuss emerging devices, applications and future research directions, underscoring the potential of MPs as integral components in next-generation spintronic and quantum information devices.