Angular Momentum Conservation and Phonon Spin in Magnetic Insulators

TL;DR

This paper presents a microscopic theory of spin-lattice interactions in magnetic insulators, highlighting phonon spin contributions and their potential dominance over magnon spin, with implications for Einstein-de Haas effects.

Contribution

It introduces a new microscopic framework that separates rigid-body rotations from phonon spin, linking couplings to measurable magnetoelastic constants, and explores phonon spin's role in angular momentum dynamics.

Findings

Phonon spin can dominate over magnon spin in excited systems.

The theory maps microscopic couplings to magnetoelastic constants.

Transient phonon spin effects can lead to Einstein-de Haas phenomena.

Abstract

We develop a microscopic theory of spin-lattice interactions in magnetic insulators, separating rigid-body rotations and the internal angular momentum, or spin, of the phonons, while conserving the total angular momentum. In the low-energy limit, the microscopic couplings are mapped onto experimentally accessible magnetoelastic constants. We show that the transient phonon spin contribution of the excited system can dominate over the magnon spin, leading to nontrivial Einstein-de Haas physics.