Efficient method for calculating magnon-phonon coupling from first principles

TL;DR

This paper introduces an efficient first-principles method to calculate magnon-phonon coupling, enabling better understanding and tuning of hybrid quasiparticles for spintronics and quantum technologies.

Contribution

The authors develop a new approach that calculates magnon-phonon coupling directly from first principles without finite differences, applicable at arbitrary wave vectors.

Findings

Accurate magnon spectra for 2D systems like CrI3 and CrTe2.

Identification of nonmagnetic atoms' role in coupling.

Potential to tune coupling via strain, doping, and terahertz excitations.

Abstract

Linear magnon-phonon coupling hybridizes magnon and phonon bands at the same energy and momentum, resulting in an anticrossing signature.This hybrid quasiparticle benefits from a long phonon lifetime and efficient magnon transport, showing great potential for spintronics and quantum information science applications.In this paper, we present an efficient and accurate first-principles approach for calculating linear magnon-phonon couplings.We first calculate the magnon spectra from linear spin wave theory with spin Hamiltonian and first-principles exchange constants, which compared well with time-dependent density-functional theory.We then obtain the magnon-phonon coupling from the derivative of off-diagonal exchange constants in real space, calculated from the Hellmann-Feynman forces of the spin-constrained configurations, avoiding the use of cumbersome finite-difference methods.Our implementation allows calculating coupling coefficients at an arbitrary wave vector in the Brillouin zone in a single step, through Fourier interpolation of real-space supercell calculations. We verify our implementation through two-dimensional magnetic systems, monolayer $\mathrm{CrI_3}$, in agreement with experiments, and extend its application to monolayer $\mathrm{CrTe_2}$. We emphasize the role of nonmagnetic atoms in superexchange interactions and magnon-phonon coupling, which have been overlooked previously. We suggest effective tuning of magnon-phonon coupling through strain, doping, and terahertz excitations, for spintronics and quantum magnonics applications.