Evolution of magnetism in the single-crystal honeycomb iridates<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>(</mml:mo><mml:msub><mml:mtext>Na</mml:mtext><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:math>Li<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow /><mml:mi>x</mml:mi></mml:msub><mml:msub><mml:mo>)</mml:mo><mml:mn>2</mml:mn></mml:msub><mml:mtext>Ir</mml:mtext><mml:msub><mml:mtext>O</mml:mtext><mml:mn>3</mml:

Contrary to the original expectation, Na2IrO3 is not a Kitaev's quantum spin liquid (QSL) but shows a zig-zag-type antiferromagnetic order in experiments. Here we propose experimental clues and criteria to measure how a material in hand is close to the Kitaev's QSL state. For this purpose, we systematically study thermal and spin excitations of a generalized Kitaev-Heisenberg model studied by Chaloupka et al. in Phys. Rev. Lett. 110, 097204 (2013) and an effective ab initio Hamiltonian for Na2IrO3 proposed by Yamaji et al. in Phys. Rev. Lett. 113, 107201 (2014), by employing a numerical diagonalization method. We reveal that closeness to the Kitaev's QSL is characterized by the following properties, besides trivial criteria such as reduction of magnetic ordered moments and Néel temperatures: (1) Two peaks in the temperature dependence of specific heat at T ℓ and T h caused by the fractionalization of spin to two types of Majorana fermions. (2) In between the double peak, prominent plateau or shoulder pinned at R 2 ln 2 in the temperature dependence of entropy, where R is the gas constant. (3) Failure of the linear spin wave approximation at the low-lying excitations of dynamical structure factors. (4) Small ratio T ℓ /T h close to or less than 0.03. According to the proposed criteria, Na2IrO3 is categorized to a compound close to the Kitaev's QSL, and is proven to be a promising candidate for the realization of the QSL if the relevant material parameters can further be tuned by making thin film of Na2IrO3 on various substrates or applying axial pressure perpendicular to the honeycomb networks of iridium ions. Applications of these characterization to (Na1−xLix)2IrO3 and other related materials are also discussed.

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“…and α-RuCl 3 29-31 , (Na 1−x Li x ) 2 IrO 3 interpolating Na 2 IrO 3 and Li 2 IrO 3 has been studied 32,33 . In Ref.…”

Section: Distance From the Kitaev Spin Liquid Phasementioning

confidence: 99%

Clues and criteria for designing a Kitaev spin liquid revealed by thermal and spin excitations of the honeycomb iridateNa2IrO3

et al. 2016

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“…Numerous theoretical studies predict the emergence of novel superconductivity with hole doping in the strong Kitaev limit [41][42][43][44][45][46][47] [59,60]. Isoelectronic substitution within the solid solution (Na,Li) 2 IrO 3 decreased the magnetic ordering temperature, although phase separation has hampered efforts to completely suppress long-range order [61][62][63].…”

mentioning

confidence: 99%

Destabilization of Magnetic Order in a Dilute Kitaev Spin Liquid Candidate

et al. 2017

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The insulating honeycomb magnet α-RuCl3 exhibits fractionalized excitiations that signal its proximity to a Kitaev quantum spin liquid (QSL) state, however, at T = 0, fragile long-range magnetic order arises from non-Kitaev terms in the Hamiltonian. Spin vacancies in the form of Ir 3+ substituted for Ru are found to destabilize this long-range order. Neutron diffraction and bulk characterization of Ru1−xIrxCl3 show that the magnetic ordering temperature is suppressed with increasing x and evidence of zizag magnetic order is absent for x > 0.3. Inelastic neutron scattering demonstrates that the signature of fractionalized excitations is maintained over the full range of x investigated. The depleted lattice without magnetic order thus hosts a spin-liquid-like ground state that may indicate the relevance of Kitaev physics in the magnetically dilute limit of RuCl3.PACS numbers: 75.30. Kz, 75.10.Kt The quantum spin liquid (QSL) holds particular fascination as a state of matter that exhibits strong quantum entanglement yet is devoid of long-range order [1, 2]. These exotic states can possess topologically protected fractionalized excitations, with possible implications for quantum information science [3, 4]. A prototypcal example is the Kitaev model on a honeycomb lattice [5], which can be solved exactly and has a QSL ground state. An effective Hamiltonian with Kitaev terms consisting of bond-directional Ising couplings may arise in spin-orbit assisted Mott insulators with J ef f = 1/2 moments in an edge-sharing octahedral environment [6]. A strong push for the experimental realization of quasi-2D honeycomb lattices showing Kitaev physics initially focused on iridate materials with the chemical formula A 2 IrO 3 [7][8][9][10], and more recently α-RuCl 3 [11][12][13][14]. Each of these compounds orders magnetically at low temperatures in a zigzag or incommensurate phase [15][16][17][18][19][20][21], and the effective low energy Hamiltonian is believed to be described by a generalized Heisenberg-Kitaev-Γ model [22][23][24][25][26][27][28][29][30][31][32][33]. Despite the appearance of long-range order, broad scattering continua observed via inelastic neutron or Raman scattering in α-RuCl 3 [13,[34][35][36] and the iridates [37] match the predicted signatures of itinerant Majorana fermions in pure Kitaev calculations [38][39][40], suggesting that these materials are proximate to the QSL state and that Kitaev interactions play an important role.In this letter, we report the evolution of the magnetic ground state in α-RuCl 3 with magnetic Ru 3+ substituted by nonmagnetic Ir 3+ , and determine a phase diagram as a function of temperature and dilution. The motivation is two-fold: to understand the role of defects in Kitaevcandidate materials and to explore avenues towards suppression of long-range order. Numerous theoretical studies predict the emergence of novel superconductivity with hole doping in the strong Kitaev limit [41][42][43][44][45][46][47] [59,60]. Isoelectronic substitution within the solid solution (Na,Li) ...

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“…Due to the much reduced atomic size of Li, its substitution for Na in (Na 1−x Li x ) 2 IrO 3 revealed that up to x = 0.25 preferentially only the Na-sites in the honeycomb plane are occupied by Li and further doping results in chemical phase segregation [18]. Magnetic properties of Na 2 IrO 3 and Li 2 IrO 3 thus differ significantly [18,19]. Due to the smaller Ir-Ir distances in the honeycomb planes in Li 2 IrO 3 , one may expect enhanced further neighbor exchange in this system.…”

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confidence: 99%

Effect of nonmagnetic dilution in the honeycomb-lattice iridatesNa2IrO3andLi2
Manni
¹
,
Tokiwa
²
,
Gegenwart
³

2014
Phys. Rev. B
65
9
64
0
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We have synthesized single crystals of Na2(Ir1−xTix)O3 and polycrystals of Li2(Ir1−xTix)O3 and studied the effect of magnetic depletion on the magnetic properties by measurements of the magnetic susceptibility, specific heat and magnetocaloric effect at temperatures down to 0.1 K. In both systems, the non-magnetic substitution rapidly changes the magnetically ordered ground state into a spin glass, indicating strong frustration. While for the Li system the Weiss temperature ΘW remains unchanged up to x = 0.55, a strong decrease |ΘW| is found for the Na system. This suggests that only for the former system magnetic exchange beyond nearest neighbors is dominating. This is also corroborated by the observation of a smeared quantum phase transition in Li2(Ir1−xTix)O3 near x = 0.5, i.e. much beyond the site percolation threshold of the honeycomb lattice.PACS numbers: 75.40. Cx, 75.10.Jm, 75.40.Gb, 75.50.Lk Iridates have attracted considerable interest in last few years due to their potential to host novel electronic and magnetic phases mediated by the combination of strong spin-orbit (SO) coupling and electronic correlations [1][2][3][4][5]. Layered honeycomb lattice iridates A 2 IrO 3 (A = Na,Li) are intensively investigated because they have been proposed as candidate materials for the realization of the highly frustrated Kitaev interaction [6] as well as correlated topological insulator phases [7,8].Both Na 2 IrO 3 and Li 2 IrO 3 are electrically insulating with fluctuating S eff = 1/2 moments above an antiferromagnetic (AF) ordering around 15 K [9,10]. Their electronic structure is discussed either within J eff = 1/2 SO Mott insulator [11] or quasi-molecular orbital (QMO) scenarios [12,13], where the upper half-filled J eff = 1/2 or QMO doublet, respectively, causes magnetism. At present the correct effective Hamiltonians for the description of magnetic exchange in the two systems are not settled. Na 2 IrO 3 displays an AF Weiss temperature of −120 K [9] and zigzag ground state [14]. Within the next-neighbor Heisenberg-Kitaev (HK) model this would require ferromagnetic (FM) Heisenberg and AF Kitaev couplings [15], which, however, seems incompatible with ab-initio DFT calculations [13]. Significant further neighbor exchange in a J 1 -J 2 -J 3 Heisenberg model has been concluded from the analysis of the measured magnon dispersion in Na 2 IrO 3 [14]. On the other hand, it has been pointed out recently, that trigonal distortions present in the system lead to an anisotropic contribution to the next neighbor exchange, which together with a FM Kitaev interaction can reproduce the experimental results [16].Isostructural honeycomb Li 2 IrO 3 displays a significantly smaller AF Weiss temperature (−30 K) compared to Na 2 IrO 3 [10]. Recent neutron scattering has detected a magnetic Bragg peak within the first Brillouin zone, indicating incommensurate spiral ordering [17]. Due to the much reduced atomic size of Li, its substitution for Na in (Na 1−x Li x ) 2 IrO 3 revealed that up to x = 0.25 preferentially only the Na-sit...

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Evolution of magnetism in the single-crystal honeycomb iridates(Na1−xLix)2IrO3

Cited by 65 publications

References 23 publications

Clues and criteria for designing a Kitaev spin liquid revealed by thermal and spin excitations of the honeycomb iridateNa2IrO3

Clues and criteria for designing a Kitaev spin liquid revealed by thermal and spin excitations of the honeycomb iridateNa2IrO3

Destabilization of Magnetic Order in a Dilute Kitaev Spin Liquid Candidate

Effect of nonmagnetic dilution in the honeycomb-lattice iridatesNa2IrO3andLi2
Manni
¹
,
Tokiwa
²
,
Gegenwart
³

2014
Phys. Rev. B
65
9
64
0
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Evolution of magnetism in the single-crystal honeycomb iridates(Na1−xLix)2IrO3

Cited by 65 publications

References 23 publications

Clues and criteria for designing a Kitaev spin liquid revealed by thermal and spin excitations of the honeycomb iridateNa2IrO3

Clues and criteria for designing a Kitaev spin liquid revealed by thermal and spin excitations of the honeycomb iridateNa2IrO3

Destabilization of Magnetic Order in a Dilute Kitaev Spin Liquid Candidate

Effect of nonmagnetic dilution in the honeycomb-lattice iridatesNa2IrO3andLi2Manni1, Tokiwa2, Gegenwart3 2014Phys. Rev. B659640View full textAdd to dashboardCite

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Effect of nonmagnetic dilution in the honeycomb-lattice iridatesNa2IrO3andLi2
Manni
¹
,
Tokiwa
²
,
Gegenwart
³

2014
Phys. Rev. B
65
9
64
0
View full text Add to dashboard Cite