Magnon-photon coupling in a non-collinear magnetic insulator Cu$_2$OSeO$_3$

TL;DR

This study demonstrates strong magnon-photon coupling in Cu$_2$OSeO$_3$, revealing complex hybridized states and phase-dependent interactions, advancing understanding of non-trivial spin textures in magnetic insulators.

Contribution

It reports the first observation of strong magnon-photon coupling in a non-collinear magnetic insulator with detailed phase-dependent behavior.

Findings

Strong coupling with cooperativity up to 3600 in ferrimagnetic phase

Dispersive coupling to helimagnon modes in conical phase

Discovery of helimagnon polariton in the helical phase

Abstract

Anticrossing behavior between magnons in a non-collinear chiral magnet Cu$_2$OSeO$_3$ and a two-mode X-band microwave resonator was studied in the temperature range 5-100K. In the field-induced ferrimagnetic phase, we observed a strong coupling regime between magnons and two microwave cavity modes with a cooperativity reaching 3600. In the conical phase, cavity modes are dispersively coupled to a fundamental helimagnon mode, and we demonstrate that the magnetic phase diagram of Cu$_2$OSeO$_3$ can be reconstructed from the measurements of the cavity resonance frequency. In the helical phase, a hybridized state of a higher-order helimagnon mode and a cavity mode - a helimagnon polariton - was found. Our results reveal a new class of magnetic systems where strong coupling of microwave photons to non-trivial spin textures can be observed.