Magnetic field-dependent low-energy magnon dynamics in $\alpha$-RuCl3

Abstract

Revealing the spin excitations of complex quantum magnets is key to developing a minimal model that explains the underlying magnetic correlations in the ground state. We investigate the low-energy magnons in $\alpha$-RuCl${}_3$ by combining time-domain terahertz spectroscopy under an external magnetic field and model Hamiltonian calculations. We observe two absorption peaks around 2.0 and 2.4 meV, which we attribute to zone-center spin waves. Using linear spin-wave theory with only nearest-neighbor terms of the exchange couplings, we calculate the antiferromagnetic resonance frequencies and reveal their dependence on an external field applied parallel to the nearest-neighbor Ru-Ru bonds. We find that the magnon behavior in an applied magnetic field can be understood only by including an off-diagonal $\Gamma$ exchange term to the minimal Heisenberg-Kitaev model. Such an anisotropic exchange interaction that manifests itself as a result of strong spin-orbit coupling can naturally account for the observed mixing of the modes at higher fields strengths.

arXiv comment13 pages, 9 figures

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• Dynamical and thermal magnetic properties of the Kitaev spin liquid candidate $\alpha$-RuCl${}_3$
• Identification of Magnetic Interactions and High-field Quantum Spin Liquid in $\alpha$-RuCl${}_3$
• Time-Domain Terahertz Spectroscopy in High Magnetic Fields
• Magnetic field-dependent low-energy magnon dynamics in $\alpha$-RuCl3
• Extraction of the interaction parameters for $\alpha -$RuCl${}_3$ from neutron data using machine learning
• Easy-plane anisotropic-exchange magnets on a honeycomb lattice: quantum effects and dealing with them
• Scattering Signatures of Bond-Dependent Magnetic Interactions
• Quantum phase transitions in the spin-1 Kitaev-Heisenberg chain
• The Saga of $\alpha$-RuCl${}_3$: Parameters, Models, and Phase Diagrams
• Field evolution of low-energy excitations in the hyperhoneycomb magnet $\beta$-Li${}_2$IrO${}_3$
• Proximate Kitaev system for an intermediate magnetic phase in in-plane magnetic fields
• Symmetry Analysis of Tensors in the Honeycomb Lattice of Edge-Sharing Octahedra
• High-field quantum spin liquid transitions and angle-field phase diagram of Kitaev magnet $\alpha$-RuCl${}_3$
• Understanding the magnetic interactions of the zig-zag honeycomb lattice: Application to $\alpha$-RuCl${}_3$
• Magnetostriction in the $J$-$K$-$\Gamma$ model: Application of the numerical linked cluster expansion
• First-principles study of bulk stacking, $J_{\mathrm{eff}}$ picture, magnetic Hamiltonian, $g$ factors, and structural distortions of $\alpha$-RuCl${}_3$
• Anomalous and Anisotropic Nonlinear Susceptibility in the Proximate Kitaev Magnet $\alpha$-RuCl${}_3$