Normal-mode splitting in the coupled system of hybridized nuclear magnons and microwave photons

TL;DR

This paper demonstrates the observation of normal-mode splitting in a hybrid nuclear-electron magnon and microwave photon system, revealing strong coupling mediated by hyperfine interactions in MnCO₃.

Contribution

First experimental observation of avoided crossing between hybridized nuclear-electron magnon modes and a microwave resonator in MnCO₃, highlighting a new class of spin-photon coupling systems.

Findings

Large magnon-photon coupling strength due to high spin density.

Observation of avoided crossing indicating strong coupling.

Hyperfine interaction mediates nuclear spin-photon coupling.

Abstract

In the weak ferromagnetic MnCO$_3$ system, a low-frequency collective spin excitation (magnon) is the hybridized oscillation of nuclear and electron spins coupled through the hyperfine interaction. By using a split-ring resonator, we performed transmission spectroscopy measurements of MnCO$_3$ system and observed, for the first time, avoiding crossing between the hybridized nuclear-electron magnon mode and the resonator mode in the NMR-frequency range. The splitting strength is quite large due to the large spin density of $^{55}$Mn, and the cooperativity value $C=0.2$ (magnon-photon coupling parameter) is close to the conditions of strong coupling. The results reveal a new class of spin systems, in which the coupling between nuclear spins and photons is mediated by electron spins via the hyperfine interaction, and in which the similar normal-mode splitting of the hybridized nuclear magnon mode and the resonator mode can be observed.