Giant Phonon Anomalies in the Proximate Kitaev Quantum Spin Liquid $\alpha$-RuCl${}_3$

Abstract

The Kitaev quantum spin liquid epitomizes an entangled topological state, for which two flavors of fractionalized low-energy excitations are predicted: the itinerant Majorana fermion and the Z2 gauge flux. Detection of these excitations remains challenging, because of their fractional quantum numbers and non-locality. It was proposed recently that fingerprints of fractional excitations are encoded in the phonon spectra of Kitaev quantum spin liquids through a novel fractional-excitation-phonon coupling. Here, we uncover this effect in $\alpha$-RuCl3 using inelastic X-ray scattering with meV resolution. At high temperature, we discover interlaced optical phonons intercepting a transverse acoustic phonon between 3 and 7 meV. Upon decreasing temperature, the optical phonons display a large intensity enhancement near the Kitaev energy, JK~8 meV, that coincides with a giant acoustic phonon softening near the Z2 gauge flux energy scale. This fractional excitation induced phonon anomalies uncover the key ingredient of the quantum thermal Hall effect in $\alpha$-RuCl3 and demonstrates a proof-of-principle method to detect fractional excitations in topological quantum materials.

References in corpus (44)

• Anyons in an exactly solved model and beyond
• Mott Insulators in the Strong Spin-Orbit Coupling Limit: From Heisenberg to a Quantum Compass and Kitaev Models
• Topological quantum chemistry
• High temperature fractional quantum Hall states
• Fractionalized excitations in the spin liquid state of a kagomé lattice antiferromagnet
• Quantum Spin Liquids
• Majorana quantization and half-integer thermal quantum Hall effect in a Kitaev spin liquid
• Proximate Kitaev Quantum Spin Liquid Behaviour in α-RuCl${}_3$
• Kitaev quantum spin liquid - concept and materialization
• Neutron tomography of magnetic Majorana fermions in a proximate quantum spin liquid
• Scattering Continuum and Possible Fractionalized Excitations in $\alpha$-RuCl${}_3$
• Physics of the Kitaev model: fractionalization, dynamical correlations, and material connections
• Evidence for a spinon Fermi surface in a triangular lattice quantum spin liquid candidate
• Excitations in the field-induced quantum spin liquid state of alpha-RuCl3
• Fermionic response from fractionalization in an insulating two-dimensional magnet
• Breakdown of Magnons in a Strongly Spin-Orbital Coupled Magnet
• Observation of Double Weyl Phonons in Parity-Breaking FeSi
• Unusual thermal Hall effect in a Kitaev spin liquid candidate $\alpha$-RuCl${}_3$
• Anomalous thermal conductivity and magnetic torque response in the honeycomb magnet $\alpha$-RuCl${}_3$
• Large field-induced gap of Kitaev-Heisenberg paramagnons in $\alpha$-RuCl${}_3$
• Choreographed entangle dances: topological states of quantum matter
• Emergence of a Field-Driven U(1) Spin Liquid in the Kitaev Honeycomb Model
• Giant thermal Hall conductivity from neutral excitations in the pseudogap phase of cuprates
• Phonons become chiral in the pseudogap phase of cuprates
• Observation of two types of anyons in the Kitaev honeycomb magnet
• Thermal Transport in the Kitaev Model
• Sample dependence of the half-integer quantized thermal Hall effect in the Kitaev candidate $\alpha$-RuCl${}_3$
• Quantization of the thermal Hall conductivity at small Hall angles
• Finite field regime for a quantum spin liquid in $\alpha$-RuCl${}_3$
• Approximately quantized thermal Hall effect of chiral liquids coupled to phonons
• Fractional Spin Fluctuation as a Precursor of Quantum Spin Liquids: Majorana Dynamical Mean-Field Study for the Kitaev Model
• Phononic Helical Nodal Lines with $\mathcal{P}\mathcal{T}$ Protection in MoB${}_2$
• Giant Kohn anomaly and the phase transition in charge density wave ZrTe_3
• Thermodynamic evidence of fractionalized excitations in α-RuCl3
• Energy Gaps and Kohn Anomalies in Elemental Superconductors
• Phonon dynamics in the Kitaev spin liquid
• Kitaev-like honeycomb magnets: Global phase behavior and emergent effective models
• Enhanced thermal Hall effect in the square-lattice Néel state
• Charge Friedel oscillations in a Mott insulator
• Electromagnon dispersion probed by inelastic x-ray scattering
• Phonon renormalization in the Kitaev quantum spin liquid
• Consideration of Thermal Hall Effect in Undoped Cuprates
• THz excitations in α-RuCl3: Majorana fermions, rigid-plane shear and compression modes
• Unquantized thermal Hall effect in quantum spin liquids with spinon Fermi surfaces

Cited by in corpus (23)

• Spin-phonon coupling driven Charge density wave in a Kagome Magnet
• Unusual heat transport of the Kitaev material Na${}_2$Co${}_2$TeO${}_6$: putative quantum spin liquid and low-energy spin excitations
• Magnetic anisotropy reversal driven by structural symmetry-breaking in monolayer α-RuCl3
• Significant thermal Hall effect in the 3$d$ cobalt Kitaev system $N{a}_{2}C{o}_{2}Te{O}_6$
• Quantum spin liquid phase in the Shastry-Sutherland model detected by an improved level spectroscopic method
• Kitaev Quantum Spin Liquids
• Extraction of the interaction parameters for $\alpha -$RuCl${}_3$ from neutron data using machine learning
• Trigonal Symmetry Breaking and its Electronic Effects in Two-Dimensional Dihalides and Trihalides
• Thermal Hall Effect in the Kitaev-Heisenberg System with Spin-Phonon Coupling
• Stacking disorder in $\alpha$-RuCl${}_3$ via x-ray three-dimensional difference pair distribution function analysis
• Emergent glassiness in disorder-free Kitaev model: Density matrix renormalization group study on a one-dimensional ladder setting
• Acoustic phonon dispersion of $\alpha$-RuCl${}_3$
• Phonon Dynamics in the Generalized Kitaev Spin Liquid
• Topological phase diagrams of in-plane field polarized Kitaev magnets
• Extended Quantum Spin Liquid with Spinon-like Excitations in an Anisotropic Kitaev-Gamma Model
• Phonon Dynamics in the Chiral Kitaev Spin Liquid
• Probing emergent QED in quantum spin ice via Raman scattering of phonons: shallow inelastic scattering and pair production
• Sound attenuation in the hyperhoneycomb Kitaev spin liquid
• Evidence for distortion-induced local electric polarization in $\alpha$-RuCl${}_3$
• A primer on Kitaev Model: Basic aspects, material realization, and recent experiments
• Deciphering competing interactions of Kitaev-Heisenberg-$\Gamma$ system in clusters: part I -- static properties
• Deciphering competing interactions of Kitaev-Heisenberg-$\Gamma$ system in clusters: part II -- dynamics of Majorana fermions
• Magnetostriction in the $J$-$K$-$\Gamma$ model: Application of the numerical linked cluster expansion