Path to stable quantum spin liquids in spin-orbit coupled correlated materials

Catuneanu, Andrei; Yamaji, Youhei; Wachtel, Gideon; Kim, Yong Baek; Kee, Hae‐Young

doi:10.1038/s41535-018-0095-2

Cited by 79 publications

(59 citation statements)

References 43 publications

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“…Although zigzag phases have been detected in Na 2 IrO 3 and α-RuCl 3 , the spin Hamiltonian of both compounds remains uncertain, and it probably involves both other anisotropic interactions and further neighbor isotropic couplings. 25,28,30,32,33,49,50 In particular, the NN off-diagonal exchange Γ may play an important role in both Na 2 IrO 3 and α-RuCl 3 , e.g. in fixing the global directions of the spins in the zigzag state at zero field.…”

Section: Discussionmentioning

confidence: 99%

Kitaev-Heisenberg model in a magnetic field: Order-by-disorder and commensurate-incommensurate transitions

et al. 2017

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We present a theoretical study of field-induced magnetic phases in the honeycomb KitaevHeisenberg model, which is believed to describe the essential physics of Mott insulators with strong spin-orbit coupling such as A2IrO3 and α-RuCl3. We obtain rich finite temperature phase diagram in which the competition between the Zeeman coupling and thermal fluctuations gives rise to both collinear zigzag phases and non-coplanar magnetic orders. Our large-scale classical MonteCarlo simulations also unveil intriguing commensurate-incommensurate transitions and multiple-Q incommensurate phases at high field. Experimental implications are also discussed.

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Section: Discussionmentioning

confidence: 99%

Kitaev-Heisenberg model in a magnetic field: Order-by-disorder and commensurate-incommensurate transitions

et al. 2017

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“…It has been shown that pure SA interactions lead to a macroscopically degenerate manifold of classical ground states in hyperhoneycomb (3D) lattices [48], a signature of frustration [29]. Quantum calculations on finite size honeycomb lattices (2D) also confirm absence of magnetic order in pure SA models [48], and it was recently suggested that this ground state continuously connects to the Kitaev QSL in the presence of bond anisotropy [32]. Our single crystal XRD experiments at high pressure show the same type of (X,Y)-and Z-bond anisotropy seen in the theoretical calculations despite the lack of exact agreement in the compressibility of the lattice parameters.…”

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confidence: 95%

“…Remarkably, ab initio calculations on anisotropically compressed lattices based on J-K-Γ spin hamiltonians (J-Heisenberg, K-Kitaev, Γ-symmetric anisotropic (SA) exchange interactions, respectively) [28] show that SA interactions become dominant at an effective pressure of P ∼ 1.4 GPa. Since pure SA models lead to largely degenerate ground states in classical models [29,30] and quantum spin liquids in quantum models [31,32], the shift in the balance of bond-directional exchange interactions driven by anisotropic compression may explain the emergence of quantum paramagnetism and provides one possible route for realization of a novel QSL state in compressed β-Li 2 IrO 3 .…”

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confidence: 99%

Pressure tuning of bond-directional exchange interactions and magnetic frustration in the hyperhoneycomb iridate β−Li2IrO3

et al. 2017

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We explore the response of Ir 5d orbitals to pressure in β-Li2IrO3, a hyperhoneycomb iridate in proximity to a Kitaev quantum spin liquid (QSL) ground state. X-ray absorption spectroscopy reveals a reconstruction of the electronic ground state below 2 GPa, the same pressure range where x-ray magnetic circular dichroism shows an apparent collapse of magnetic order. The electronic reconstruction, which manifests a reduction in the effective spin-orbit (SO) interaction in 5d orbitals, pushes β-Li2IrO3 further away from the pure J eff = 1/2 limit. Although lattice symmetry is preserved across the electronic transition, x-ray diffraction shows a highly anisotropic compression of the hyperhoneycomb lattice which affects the balance of bond-directional Ir-Ir exchange interactions driven by spin-orbit coupling at Ir sites. An enhancement of symmetric anisotropic exchange over Kitaev and Heisenberg exchange interactions seen in theoretical calculations that use precisely this anisotropic Ir-Ir bond compression provides one possible route to realization of a QSL state in this hyperhoneycomb iridate at high pressures.The novel electronic ground states of 5d-based compounds driven by spin-orbit interactions continue to provide an excellent playground for the realization of unconventional quantum phases of matter including topological insulators [1-4] and quantum spin-liquids (QSLs) [5][6][7]. One example of the latter is the non-trivial QSL ground state of the Kitaev model [8], a rare example of a solvable interacting quantum model with Majorana fermions as its elementary excitations. Material candidates for possible realization of the Kitaev model include honeycomb-based-lattice systems with strong spin-orbit coupling [6,9], such as the two and three-dimensional honeycomb iridates, α-Li(Na) [7,[20][21][22] as well as α-RuCl 3 [23,24]. However, it is experimentally established that these materials order magnetically at low temperatures [17,18,20,[25][26][27], spoiling numerous attempts to realize the Kitaev QSL. Hence, tuning structure and related intricate interactions present in these materials through chemical or physical pressure provides a potential route to introduce magnetic frustration and realize novel phases of matter.In this Letter we have investigated the electronic and structural response of β-Li 2 IrO 3 to high pressure. Xray absorption near edge structure (XANES) measurements at Ir L-edges reveal a dramatic suppression of the isotropic Ir (L 3 /L 2 ) branching ratio at P ∼ 1.5 GPa, signaling a reduction in the effective strength of spinorbit interactions in the 5d band. This is the same pressure at which net magnetization in applied field collapses [17]. The reconstructed electronic state preserves the L z / S z orbital-to-spin moment ratio of Ir magnetic moments and the insulating ground state indicating that spin-orbit interactions and Mott physics con-

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“…In these candidate materials, as with other QSL candidates, the presence of additional symmetry allowed terms (Heisenberg and bond-dependent off-diagonal interactions in this case), produces long range magnetic order. 10,10,29,37 Despite extensive studies and evidence for fractional particles 11,34,38,39 , the relative size of the non-Kitaev terms and the range over which they are relevant remains controversial 37,40 . In α-RuCl 3 , these non-Kitaev terms lead to a magnetically ordered phase below 7 K, which could be destroyed by an in-plane magnetic field [41][42][43][44][45] .…”

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confidence: 99%

The range of non-Kitaev terms and fractional particles in α-RuCl3

Wang

Osterhoudt

Tian³

et al. 2020

npj Quantum Mater.

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Significant efforts have focused on the magnetic excitations of relativistic Mott insulators, predicted to realize the Kitaev quantum spin liquid (QSL). This exactly solvable model involves a highly entangled state resulting from bond-dependent Ising interactions that pro-1 arXiv:2003.09274v1 [cond-mat.str-el] 18 Mar 2020 duce excitations which are non-local in terms of spin flips. A key challenge in real materials is identifying the relative size of the non-Kitaev terms and their role in the emergence or suppression of fractional excitations. Here, we identify the energy and temperature boundaries of non-Kitaev interactions by direct comparison of the Raman susceptibility of α-RuCl 3 with quantum Monte Carlo (QMC) results for the Kitaev QSLs. Moreover, we further confirm the fractional nature of the magnetic excitations, which is given by creating a pair of fermionic quasiparticles. Interestingly, this fermionic response remains valid in the non-Kitaev range. Our results and focus on the use of the Raman susceptibility provide a stringent new test for future theoretical and experimental studies of QSLs. Exotic excitations with fractional quantum numbers are a key characteristic of QSLs 1-4 , which result from the long range entanglement of these non-trivial topological phases 5-7 . Originating from frustrated magnetic interactions, the fractional nature inspires an overarching goal of studying QSLs, realizing topological quantum computing immune to decoherence, with high operating temperatures from large exchange interactions 8, 9 . The last decade has seen great progress towards identifying the fractional excitations of QSLs 10-18 . Attention has focused on relativistic Mott insulators that are close to the exactly solvable Kitaev model with a QSL ground state. In materials such as A 2 IrO 3 (A = Cu, Li or Na) 4, 8, 19-23 and α-RuCl 3 24-27 , the large spin-orbit coupling and Coulomb repulsion result in j ef f = 1/2 moments on a honeycomb lattice 2, 9, 28-35 .According to the pure Kiteav model, in these materials spin flips could produce Z 2 gauge fluxes and dispersive Majorana fermions. 14, 36 .

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Path to stable quantum spin liquids in spin-orbit coupled correlated materials

Cited by 79 publications

References 43 publications

Kitaev-Heisenberg model in a magnetic field: Order-by-disorder and commensurate-incommensurate transitions

Kitaev-Heisenberg model in a magnetic field: Order-by-disorder and commensurate-incommensurate transitions

Pressure tuning of bond-directional exchange interactions and magnetic frustration in the hyperhoneycomb iridate β−Li2IrO3

The range of non-Kitaev terms and fractional particles in α-RuCl3

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