First-principles calculations of linear magnon-phonon coupling in two-dimensional van der Waals ferromagnets

Linear magnon-phonon coupling hybridizes the magnon and phonon band at the same energy and wavevector, resulting in an opening gap and an anticrossing feature. This hybrid quasi-particle has the advantage of long lifetime from phonon and efficient transport from magnon, showing great potential for spintronics applications [1]. In this talk, we present our first-principles approach to calculating linear magnon-phonon coupling. We derive the formula from a spin Hamiltonian based on an explicit dependence on phonon displacement [2]. Magnon eigenstates are computed from linear spin wave theory. The linear-magnon coupling matrix is obtained from the derivative of the off-diagonal exchange constants in real space. Our implementation allows for calculating coupling constant at arbitrary wavevector in the Brilloin zone in a single step, through Fourier interpolation of real-space supercell calculations. The derivatives are calculated through the forces using the spin constrained DFT calculations, eliminating the use of cumbersome finite-difference calculations. We verify our implementation using monolayer CrI3 and extend its application to monolayer CrTe2. We compare the magnon spectra computed from linear spin wave theory and time-dependent density functional theory. We also study the strain effect on linear magnon-phonon coupling in CrTe2.