Hybrid magnonics in hybrid perovskite antiferromagnets

Abstract

Hybrid magnonic systems are a newcomer for pursuing coherent information processing owing to their rich quantum engineering functionalities. One prototypical example is hybrid magnonics in antiferromagnets with an easy-plane anisotropy that resembles a quantum-mechanically mixed two-level spin system through the coupling of acoustic and optical magnons. Generally, the coupling between these orthogonal modes is forbidden due to their opposite parity. Here we show that the Dzyaloshinskii-Moriya-Interaction (DMI), a chiral antisymmetric interaction that occurs in magnetic systems with low symmetry, can lift this restriction. We report that layered hybrid perovskite antiferromagnets with an interlayer DMI can lead to a strong intrinsic magnon-magnon coupling strength up to 0.24 GHz, which is four times greater than the dissipation rates of the acoustic/optical modes. Our work shows that the DMI in these hybrid antiferromagnets holds promise for leveraging magnon-magnon coupling by harnessing symmetry breaking in a highly tunable, solution-processable layered magnetic platform.

Fig. 1. Magnetic properties of a hybrid perovskite antiferromagnet.

a Schematic illustration of the acoustic and optical modes in a two-sublattice easy-plane antiferromagnet that are protected from interacting by parity. b A sketch of the inherently low symmetry of the Cu-EA structure due to octahedral tilting and the spin ordering of the layered antiferromagnet and its sublattice structure. c Magnetic properties of Cu-EA at T = 2.5 K. M(H) loops are obtained along all three principal axes of the single crystal up to saturation region. The upper inset shows the spin-flop transition at low field at $∣{\mathbf{H}}_{\mathbf{ext}}∣=30\mathrm{mT}$. M vs. T is included in the lower inset to show the onset of magnetic ordering at the transition temperature, T ~ 10 K.

Fig. 2. Antiferromagnetic resonance in Cu-EA single crystals with a strong magnon–magnon coupling induced by the DMI.

a Schematic illustrations of the parallel and transverse pumping geometries for selectively exciting the optical and acoustic modes when the external magnetic field is applied parallel and perpendicular to the microwave RF field, ${\mathbf{h}}_{\mathbf{rf}}$. b Schematic illustrations of the broken symmetry (${\mathbf{H}}_{\mathbf{ext}}\parallel \mathbf{D}$) and symmetric (${\mathbf{H}}_{\mathbf{ext}}\perp \mathbf{D}$) pumping configurations when the external magnetic field is applied parallel and perpendicular to the DMI vector of the Cu-EA single crystal. c–f antiferromagnetic resonance spectra collected under the four possible experimental geometries as described in a and b. Insets in c–f show the resonance spectra under an adjusted color scale to elucidate the presence of dark modes at high fields.

Fig. 3. Enhanced magnon–magnon coupling strength.

a Enhancement of the anticrossing gap by by rotating the external magnetic field by an oblique angle Θ along the out-of-plane direction at $45^{\circ }$ to the in-plane principal a-axis as indicated. b $\mathrm{\Theta }$ dependence of the coupling strength $g_c$ and the dissipation rates for the upper and lower magnonic branches, ${\kappa }_U$ and ${\kappa }_L$ derived from the frequency-field dependence of resonance spectra presented in (c). The dotted red line is the fitted curve for the coupling strength following a quadratic behavior. The insets in (c) highlight the resonance spectra under an adjusted color scale, showing the increased DMI-induced nonzero gap, $f_g$ of the ‘dark’ mode as $\mathrm{\Theta }$ increases.