Terahertz cavity magnon polaritons

TL;DR

This study demonstrates strong terahertz photon-magnon coupling in antiferromagnetic NiO within a cavity, revealing potential for terahertz spintronics and quantum technologies.

Contribution

First observation of resonant photon-magnon coupling above 1 THz in a room-temperature antiferromagnetic insulator NiO using a self-formed Fabry-Pérot cavity.

Findings

Clear vacuum Rabi splittings observed exceeding linewidths

Photon-magnon anticrossing demonstrated in terahertz range

NiO shows promise for terahertz cavity magnonics

Abstract

Hybrid light-matter coupled states, or polaritons, in magnetic materials have attracted significant attention due to their potential for enabling novel applications in spintronics and quantum information processing. However, most studies to date have been carried out for ferromagnetic materials with magnon excitations at gigahertz frequencies. Here, we have investigated strong resonant photon-magnon coupling at frequencies above 1 terahertz for the first time in a prototypical room-temperature antiferromagnetic insulator, NiO, inside a Fabry-P\'erot cavity. The cavity was formed by the crystal itself when it was thinned down to an optimized thickness. By using terahertz time-domain spectroscopy in high magnetic fields up to 25 T, we swept the magnon frequency through Fabry-P\'erot cavity modes and observed photon-magnon anticrossing behavior, demonstrating clear vacuum Rabi splittings exceeding the polariton linewidths. These results show that NiO is a promising platform for exploring antiferromagnetic spintronics and cavity magnonics in the terahertz frequency range.