# Gigahertz frequency antiferromagnetic resonance and strong magnon-magnon coupling in the layered crystal CrCl3

## TL;DR

This study investigates GHz-frequency antiferromagnetic resonances in layered CrCl3, revealing optical and acoustic modes, symmetry-protected crossings, and tunable magnon-magnon coupling, advancing understanding of 2D magnetic dynamics.

## Contribution

It demonstrates the observation of both optical and acoustic antiferromagnetic resonances and tunable magnon-magnon coupling in a layered 2D antiferromagnet, which was not previously reported.

## Key findings

- Observation of GHz-range optical and acoustic resonance modes.
- Identification of symmetry-protected crossing between modes.
- Induction of strong, tunable magnon-magnon coupling.

## Abstract

We report broadband microwave absorption spectroscopy of the layered antiferromagnet CrCl3. We observe a rich structure of resonances arising from quasi-two-dimensional antiferromagnetic dynamics. Due to the weak interlayer magnetic coupling in this material, we are able to observe both optical and acoustic branches of antiferromagnetic resonance in the GHz frequency range and a symmetry-protected crossing between them. By breaking rotational symmetry, we further show that strong magnon-magnon coupling with large tunable gaps can be induced between the two resonant modes.