Terahertz excitations in 
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: Majorana fermions and rigid-plane shear and compression modes

Reschke, S.; Tsurkan, V.; Do, Seung-Hwan; Choi, Kwang‐Yong; Lunkenheimer, P.; Wang, Zhe; Loidl, A.

doi:10.1103/physrevb.100.100403

Cited by 24 publications

(22 citation statements)

References 45 publications

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“…2c . Two low-energy optical phonons, P 1 and P 2 , are observed at the Brillouin zone center Γ 2 , corresponding to and meV, which are in good agreement with previous optical and neutron studies 19 , 40 . The two optical phonons carry opposite phonon velocities and form an interlaced structure that intercepts the acoustic phonon.…”

Section: Resultssupporting

confidence: 91%

Giant phonon anomalies in the proximate Kitaev quantum spin liquid α-RuCl3

Zhang

Said

et al. 2021

Nat Commun

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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. 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 detect anomalous phonon effects in α-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. These phonon anomalies signify the coupling of phonon and Kitaev magnetic excitations in α-RuCl3 and demonstrates a proof-of-principle method to detect anomalous excitations in topological quantum materials.

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Section: Resultssupporting

confidence: 91%

Giant phonon anomalies in the proximate Kitaev quantum spin liquid α-RuCl3

Zhang

Said

et al. 2021

Nat Commun

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“…In light of our results we thus expect the Kitaev and off-diagonal couplings strengths to be larger, and that α-RuCl 3 may be closer to the QSL regime than previously believed. (We note that recent anisotropic susceptibility [66] and THz spectroscopy experiments [41] are also consistent with higher Kitaev strengths than in Model 2.) In contrast, the calculated dynamical spin structure factors and INS intensities are much more sensitive to the relative strengths of different interaction terms.…”

Section: Discussionsupporting

confidence: 75%

“…The quantization occurs in a narrow range of in-plane magnetic fields, where the magnetic order is melted, possibly uncovering an intermediate QSL state [24,[29][30][31][32]. Further evidence for Kitaev physics has been found in experiments reporting troscopy results [40][41][42]. Altogether, these experiments strongly suggest that α-RuCl 3 can be described by a generalized Kitaev-Heisenberg Hamiltonian [13,14], including off-diagonal and furtherrange interactions.…”

Section: Introductionmentioning

confidence: 96%

Dynamical and thermal magnetic properties of the Kitaev spin liquid candidate α-RuCl3

Laurell

Okamoto

2020

npj Quantum Mater.

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What is the correct low-energy spin Hamiltonian description of α-RuCl 3 ? The material is a promising Kitaev spin liquid candidate, but is also known to order magnetically, the description of which necessitates additional interaction terms. The nature of these interactions, their magnitudes and even signs, remain an open question. In this work we systematically investigate dynamical and thermodynamic magnetic properties of proposed effective Hamiltonians. We calculate zero-temperature inelastic neutron scattering (INS) intensities using exact diagonalization, and magnetic specific heat using a thermal pure quantum states method. We find that no single current model satisfactorily explains all observed phenomena of α-RuCl 3 . In particular, we find that Hamiltonians derived from first principles can capture the experimentally observed high-temperature peak in the magnetic specific heat, while overestimating the magnon energy at the zone center. In contrast, other models reproduce important features of the INS data, but do not adequately describe the magnetic specific heat. 1, 4 2 3 5 6 7 8 9 10 11 14 15 16 17 (c) Spread of proposed models FIG. 1. α-RuCl 3 . (a) The zigzag magnetic order. (b) The honeycomb lattice and its different bonds. Solid, dotted and dashed lines represent nearest, second-nearest and third-nearest neighbor bonds, respectively. (c) The variability in two nearest neighbor (NN) parameters between various proposed spin Hamiltonians for α-RuCl 3 .The Hamiltonians marked by red, bold numbers (blue, roman) are discussed in the main text (Supplemental Information). Here K 1 and J 1 are the NN Kitaev and Heisenberg couplings, respectively, and Γ is an NN symmetric off-diagonal interaction. Models with ferromagnetic (antiferromagnetic) K 1 are marked with crosses (open circles). Bond averaged values were used for anisotropic models. magnetic specific heat [25, 33, 34], NMR [30, 35], microwave absorption [36], Raman scattering [37-39], and THz spec-arXiv:1906.07579v1 [cond-mat.str-el]

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“…The pure Kitaev model features a spin-liquid ground state characterized by fractionalized excitations [2], but the majority of materials reported to date are magnetically ordered in zero field, because additional interactions beyond the Kitaev term are present [3]. Nevertheless, at least one of these materials, α-RuCl 3 , reveals not only magnon excitations at low energies [4][5][6][7], but also a peculiar excitation continuum at higher energies [8][9][10][11]. This continuum is sometimes interpreted as a vestige of spin-liquid physics of the pure Kitaev model [12], although a more mundane explanation in terms of magnon breakdown caused by anisotropic terms in the spin Hamiltonian appears equally plausible and even better justified microscopically [13,14].…”

Section: Introductionmentioning

confidence: 99%

Field evolution of low-energy excitations in the hyperhoneycomb magnet β−Li2IrO3

et al. 2020

Self Cite

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Li nuclear magnetic resonance and terahertz (THz) spectroscopies are used to probe magnetic excitations and their field dependence in the hyperhoneycomb Kitaev magnet β-Li 2 IrO 3. Spin-lattice relaxation rate (1/T 1) measured down to 100 mK indicates the gapless nature of the excitations at low fields (below H c 2.8 T), in contrast to the gapped magnon excitations found in the honeycomb Kitaev magnet α-RuCl 3 at zero applied magnetic field. At higher temperatures in β-Li 2 IrO 3 , 1/T 1 passes through a broad maximum without any clear anomaly at the Néel temperature T N 38 K, suggesting the abundance of low-energy excitations that are indeed observed as two peaks in the THz spectra; both correspond to zone-center magnon excitations. At higher fields (above H c), an excitation gap opens, and a redistribution of the THz spectral weight is observed without any indication of an excitation continuum, in contrast to α-RuCl 3 where an excitation continuum was reported.

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Terahertz excitations in α−RuCl3 : Majorana fermions and rigid-plane shear and compression modes

Cited by 24 publications

References 45 publications

Giant phonon anomalies in the proximate Kitaev quantum spin liquid α-RuCl3

Giant phonon anomalies in the proximate Kitaev quantum spin liquid α-RuCl3

Dynamical and thermal magnetic properties of the Kitaev spin liquid candidate α-RuCl3

Field evolution of low-energy excitations in the hyperhoneycomb magnet β−Li2IrO3

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