Kineo-Elasticity and Nonreciprocal Phonons by Rashba-induced Interfacial Spin-Lattice Coupling

TL;DR

This paper uncovers a novel interfacial spin-lattice coupling analogous to Rashba spin-orbit interaction, leading to nonreciprocal phonon propagation in magnetic heterostructures with potential applications in phononic devices.

Contribution

It introduces a new type of spin-lattice coupling enabled by broken inversion symmetry, revealing its effects on phonon nonreciprocity and hybridization in magnetic heterostructures.

Findings

Nonreciprocal transverse phonon velocity due to interfacial coupling

Directional hybridization and absorption in magnon-phonon spectrum

Asymmetric phonon propagation lengths for opposite directions

Abstract

We identify a previously unrecognized spin-lattice coupling that is allowed in the presence of broken inversion symmetry that can be considered as a lattice analogue to the electronic Rashba spin-orbit coupling. In the low-frequency regime with magnons integrated out, the interfacial spin-lattice coupling is shown to engender a kineo-elastic term in the phonon Lagrangian that couples the strain on the lattice to its velocity and thereby gives rise to a nonreciprocity in transverse phonon velocity. We further analyze the full magnon-phonon spectrum and uncover directional hybridization and absorption, leading to asymmetric phonon propagation lengths for opposite directions. Our results indicate that such interfacial spin-lattice coupling can serve as an efficient route to achieve nonreciprocal phonon propagation properties in magnetic heterostructures with strong Rashba spin-orbit coupling.