Coupled Spin-Light dynamics in Cavity Optomagnonics

TL;DR

This paper derives the microscopic Hamiltonian for cavity optomagnonics, explores the nonlinear classical dynamics of a macrospin under optical coupling, and reveals phenomena like optically induced damping, self-sustained oscillations, and chaos.

Contribution

It provides the first microscopic derivation of the optomagnonic Hamiltonian and analyzes the nonlinear dynamics, including chaos, in optical cavity-magnetization systems.

Findings

Large optomagnonic coupling in the linear regime.

Optically induced damping can change sign, causing self-sustained oscillations.

System exhibits chaotic behavior through period doubling.

Abstract

Experiments during the past two years have shown strong resonant photon-magnon coupling in microwave cavities, while coupling in the optical regime was demonstrated very recently for the first time. Unlike with microwaves, the coupling in optical cavities is parametric, akin to optomechanical systems. This line of research promises to evolve into a new field of optomagnonics, aimed at the coherent manipulation of elementary magnetic excitations by optical means. In this work we derive the microscopic optomagnonic Hamiltonian. In the linear regime the system reduces to the well-known optomechanical case, with remarkably large coupling. Going beyond that, we study the optically induced nonlinear classical dynamics of a macrospin. In the fast cavity regime we obtain an effective equation of motion for the spin and show that the light field induces a dissipative term reminiscent of Gilbert damping. The induced dissipation coefficient however can change sign on the Bloch sphere, giving rise to self-sustained oscillations. When the full dynamics of the system is considered, the system can enter a chaotic regime by successive period doubling of the oscillations.