Coupling microwave photons to topological spin textures in Cu2OSeO3

Abstract

Topologically protected nanoscale spin textures, known as magnetic skyrmions, possess particlelike properties and feature emergent magnetism effects. In bulk cubic helimagnets, distinct skyrmion resonant modes are already identified using a technique such as ferromagnetic resonance in spintronics. However, direct light-matter coupling between microwave photons and skyrmion resonance modes still needs to be demonstrated. Utilizing two distinct cavity systems, we observe a direct interaction between the cavity resonant mode and two resonant skyrmion modes, the counterclockwise gyration and breathing modes, in bulk Cu 2 OSeO 3 . For both resonant modes, we find the largest coupling strength at 57 K indicated by an enhancement of the cavity linewidth at the degeneracy point. We study the effective coupling strength as a function of temperature within the expected skyrmion phase. We attribute the maximum in effective coupling strength to the presence of a large number of skyrmions, and correspondingly to a completely stable skyrmion lattice. Our experimental findings indicate that the coupling between photons and resonant modes of magnetic skyrmions depends on the relative density of these topological particles instead of the pure spin number in the system.

Magnetoelectric Cavity Magnonics in Skyrmion Crystals

“…4(a) of the main text. In contrast, when 𝜅 𝑛 > |𝑔 CCW m-el |, the hybridization gap becomes less pronounced [41]. However, we can still see that |𝑆 11 (𝜔)| 2 is increased significantly when the CCW and breathing modes intersect with the cavity mode, as shown in Fig.…”

“…In the previous experiments, the parameters were chosen as 𝜂 ≈ 0.03 and Ω/(2𝜋) = 1.1 GHz in Ref. [41] and 𝜂 ≈ 0.06 and Ω/(2𝜋) = 0.68 GHz in Ref. [42], where |𝑔 CCW m-mag |/(2𝜋) was found to be approximately 120 MHz in both references.…”

“…11(a)-(c). Noting that the damping rates for CCW and breathing modes were estimated approximately as 300 MHz for CCW and breathing modes in the high-temperature SkX phase [41,42], the strong coupling regime can be realized in the low-temperature SkX phase.…”

“…We reveal that the resulting MP coupling is strongly anisotropic with respect to magnetization reversal, establishing a means for exceptional tunability. We make quantitative predictions for the multiferroic skyrmion host Cu 2 OSeO 3 that recently drew a lot of interest in the context of cavity magnonics [40][41][42]. In the ferromagnetic phase of Cu 2 OSeO 3 , the MP anisotropy can be so strong that MP coupling is absent for one magnetization direction but leading to strong coupling for the opposite direction.…”

Probing spin dynamics of ultra-thin van der Waals magnets via photon-magnon coupling

“…Here, S 0 is the microwave transmission baseline, A the peak amplitude, q describes the asymmetry of the lineshape and κ eff represents the effective loss rate of the hybrid system. ω res experiences a dispersive shift when the photon mode and the magnon mode hybridize, indicating an onset of a strong interaction between the two individual systems 19,22,[32][33][34] . The observation of a continuous dispersive shift with no clear mode separation suggests that the hybrid system resides in a regime of high cooperativity 19,33 (we discuss a quantitative analysis later).…”