Evidence for Topological Magnon–Phonon Hybridization in a 2D Antiferromagnet down to the Monolayer Limit

Abstract

Topological phonons and magnons potentially enable low-loss, quantum coherent, and chiral transport of information and energy at the atomic scale. Van der Waals magnetic materials are promising to realize such states due to their recently discovered strong interactions among the electronic, spin, and lattice degrees of freedom. Here, we report the first observation of coherent hybridization of magnons and phonons in monolayer antiferromagnet FePSe3 by cavity-enhanced magneto-Raman spectroscopy. The robust magnon–phonon cooperativity in the 2D limit occurs even in zero magnetic field, which enables nontrivial band inversion between longitudinal and transverse optical phonons caused by the strong coupling with magnons. The spin and lattice symmetry theoretically guarantee magnetic-field-controlled topological phase transition, verified by nonzero Chern numbers calculated from the coupled spin–lattice model. The 2D topological magnon–phonon hybridization potentially offers a new route toward quantum phononics and magnonics with an ultrasmall footprint.

Direct observation of topological magnon polarons in a multiferroic material

“…We note that a recent magneto-Raman scattering study 43 has reported the existence of topological magnon polarons due to the zigzag antiferromagnetic order in the monolayer FePSe 3 , where the magnon-phonon coupling originates from the anisotropic exchange interactions 43 . It implies that the topological nature of band-inverted magnon polarons can be inherent and resilient, irrespective of the particular form of magnon-phonon coupling 9 – 15 .…”

Two-dimensional materials for future information technology: status and prospects

“…Following the above two manners, the magnetic-mediated magnon and phonon behaviors are demonstrated by magneto-Raman spectra in the prototypical A-type 2D antiferromagnets CrI3 [277,278,[285][286][287] (as shown in Figure 23(n)) and CrBr3 [283], and in interlayer intrinsic 2D antiferromagnets FePS3 (as shown in Figure 23(o)) [288] and FePSe3 (as shown in Figure 23(p)) [288,289]. Compared to Kerr rotation, the magneto-optical Raman effects from the A1g phonons in CrBr3 and CrI3 are extraordinarily enhanced by two orders (rotation of 40 • ), which are nonlinear and nonreciprocal versus magnetic field.…”

Mode‐Selective Spin–Phonon Coupling in van der Waals Antiferromagnets

“…[8][9][10] There are recent reports of magnons (spin waves) in these materials [11,12] as well as observations of coupling between magnons, phonons and excitons. [13][14][15][16][17][18] These phenomena underpin the physics of emergent and future devices based on the MPX 3 materials, making it important to understand and control them. [19] Thus far, magnon-phonon coupling in MPX 3 compounds has been observed both in the presence and absence of externally applied magnetic fields; this coupling typically occurs below T N where the spins are locked in.…”

“…Below T N , the magnons have been observed to interact with Raman and infrared-active phonons with frequencies between 100 and 600 cm −1 (or ∼3-18 THz). These coupling and hybridization effects have been observed through Raman and infrared spectroscopy, [13][14][15]20] as well as THz pump-probe spectroscopy. [18] Temperature-dependent Raman spectroscopy measurements in particular have revealed insights into spin-phonon coupling in FePS 3 , FePSe 3 , NiPS 3 and MnPSe 3 through large changes in peak intensities, frequencies and widths upon cooling the material below T N .…”