Interlayer Dzyaloshinskii-Moriya interactions induced via nonlinear phononics in bilayer van der Waals materials

We theoretically study the impact of light-driven structural changes via nonlinear phononics on the magnetic order of untwisted bilayer van der Waals materials. We consider an illustrative example of the AA-stacked bilayer honeycomb lattice and show that high-intensity light in resonance with selected phonons induces large-amplitude phonon displacements that modify the magnetic Hamiltonian of the system. We perform a group theory analysis to identify the vibrational modes of the honeycomb bilayer and the nonlinear couplings among them in the strongly driven regime. We find that the structural changes in the strongly driven regime lower the symmetry relative to the equilibrium lattice and produce changes in the magnetic interactions between the local moments. In particular, the lattice symmetry changes permit a nonzero interlayer Dzyaloshinskii-Moriya interaction that induces a magnetic state with canted local moments. Using a spin-wave analysis around the new magnetic configuration, we study the corresponding changes in the magnon spectrum and identify a protocol for engineering topological band transitions using a combination of nonlinear phononics and an external magnetic field. Our paper suggests a strategy to induce and control interlayer Dzyaloshinskii-Moriya interactions in a class of layered van der Waals materials, the effect of which is to modify the magnetic ground state, magnon dispersions, and related band geometric properties, including topological invariants.