Signatures of low-energy fractionalized excitations in $\alpha$-RuCl${}_3$ from field-dependent microwave absorption

Abstract

Topologically ordered states of matter are generically characterized by excitations with quantum number fractionalization. A prime example is the spin liquid realized in Kitaev's honeycomb-lattice compass model where spin-flip excitations fractionalize into Majorana fermions and Ising gauge fluxes. While numerous compounds have been proposed to be proximate to such a spin-liquid phase, clear-cut evidence for fractionalized excitations is lacking. Here we employ microwave absorption measurements to study the low-energy excitations in $\alpha$-RuCl${}_3$ over a wide range of frequencies, magnetic fields, and temperatures, covering in particular the vicinity of the field-driven quantum phase transition where long-range magnetic order disappears. In addition to conventional gapped magnon modes we find a highly unusual broad continuum characteristic of fractionalization which -- most remarkably -- extends to energies below the lowest sharp mode and to temperatures significantly higher than the ordering temperature, and develops a gap of a nontrivial origin in strong magnetic fields. Our results unravel the signatures of fractionalized excitations in $\alpha$-RuCl${}_3$ and pave the way to a more complete understanding of the Kitaev spin liquid and its instabilities.

revised version

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• Field evolution of magnons in $\alpha$-RuCl${}_3$ by high-resolution polarized terahertz spectroscopy
• Field induced magnon excitation and in gap absorption of Kitaev candidate RuCl3
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Cited by in corpus (44)

• A Field Guide to Spin Liquids
• Orbital effects in solids: basics, recent progress and opportunities
• The planar thermal Hall conductivity in the Kitaev magnet α-RuCl3
• Finite field regime for a quantum spin liquid in $\alpha$-RuCl${}_3$
• Heisenberg-Kitaev physics in magnetic fields
• Ferrimagnetism and anisotropic phase tunability by magnetic fields in Na${}_2$Co${}_2$TeO${}_6$
• Dynamical and thermal magnetic properties of the Kitaev spin liquid candidate $\alpha$-RuCl${}_3$
• High-Field Quantum Disordered State in $\alpha$-RuCl3: Spin Flips, Bound States, and a Multi-Particle Continuum
• Unusual heat transport of the Kitaev material Na${}_2$Co${}_2$TeO${}_6$: putative quantum spin liquid and low-energy spin excitations
• The range of non-Kitaev terms and fractional particles in RuCl${}_3$
• Thermodynamic perspective on the field-induced behavior of $\alpha$-RuCl${}_3$
• Giant magnetic in-plane anisotropy and competing instabilities in Na3Co2SbO6
• Nature of Magnetic Excitations in the High-Field Phase of $\alpha$-RuCl${}_3$
• Electrical probes of the non-Abelian spin liquid in Kitaev materials
• Field-induced phase transitions of the Kitaev material $\alpha$-RuCl${}_3$ probed by thermal expansion and magnetostriction
• Angle-dependent thermodynamics of $\alpha$-RuCl${}_3$
• Observation of a random singlet state in a diluted Kitaev honeycomb material
• Spin-glass state and reversed magnetic anisotropy induced by Cr doping in the Kitaev magnet $\alpha$-RuCl${}_3$
• Kitaev Quantum Spin Liquids
• High-field thermal transport properties of the Kitaev quantum magnet alpha-RuCl3: evidence for low-energy excitations beyond the critical field
• Extraction of the interaction parameters for $\alpha -$RuCl${}_3$ from neutron data using machine learning
• Majorana-Magnon Crossover by a Magnetic Field in the Kitaev Model: Continuous-Time Quantum Monte Carlo Study
• Investigation of the magnetoelastic coupling anisotropy in the Kitaev material $\alpha$-RuCl${}_3$
• Possible Intermediate Quantum Spin Liquid Phase in $\alpha$-RuCl${}_3$ under High Magnetic Fields up to 100 T
• Theory of electronic magnetoelectric coupling in $d^5$ Mott insulators
• Probing quantum spin liquids with a quantum twisting microscope
• Phononic-magnetic dichotomy of the thermal Hall effect in the Kitaev-Heisenberg candidate material Na${}_2$Co${}_2$TeO${}_6$
• 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
• Magnetic anisotropy and low-energy spin dynamics in the van der Waals compounds Mn${}_2$P${}_2$S${}_6$ and MnNiP${}_2$S${}_6$
• Neutron spectroscopy evidence for a possible magnetic-field-induced gapless quantum-spin-liquid phase in a Kitaev material $\alpha$-RuCl${}_3$
• Anomalous thermal relaxation and pump-probe spectroscopy of 2D topologically ordered systems
• Static magnetic and ESR spectroscopic properties of the dimer-chain antiferromagnet BiCoPO${}_5$
• Phase diagram and thermal Hall conductivity of spin-liquid Kekulé-Kitaev model
• Dilution of the magnetic lattice in the Kitaev candidate $\alpha$-RuCl${}_3$ by Rh${}^{3+}$ doping
• Evidence for distortion-induced local electric polarization in $\alpha$-RuCl${}_3$
• A quantum Monte Carlo method on asymptotic Lefschetz thimbles for quantum spin systems: An application to the Kitaev model in a magnetic field
• Field tuning Kitaev systems for spin fractionalization and topological order
• The Kekulé-Kitaev model: linear and non-linear responses and magnetic field effects
• Scaling behavior and giant field-enhancement of the thermal conductivity in the honeycomb antiferromagnet BaCo2(AsO4)2
• Anomalous and Anisotropic Nonlinear Susceptibility in the Proximate Kitaev Magnet $\alpha$-RuCl${}_3$
• The Role of the Third Dimension in Searching Majorana Fermions in $\alpha$-RuCl${}_3$ via Phonons
• The field-angle anisotropy of proximate Kitaev systems under an in-plane magnetic field
• Spin-orbit coupling controlled two-dimensional magnetism in chromium trihalides