Spin-Orbital Short-Range Order on a Honeycomb-Based Lattice

Nakatsuji, Satoru; Kuga, Kentaro; Kimura, Kazuhiro; Satake, R.; Katayama, Naoyuki; Nishibori, Eiji; Sawa, Hiroshi; Ishii, Ryuta; Hagiwara, Masayuki; Bridges, F.; Ito, Takashi U.; Higemoto, Wataru; Karaki, Yoshitomo; Halim, Mario; Nugroho, A. A.; Rodríguez-Rivera, J. A.; Green, Mark; Broholm, C.

doi:10.1126/science.1212154

Cited by 141 publications

(304 citation statements)

References 35 publications

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“…One issue that has been persistent among these systems, such as Ba 3 CuSb 2 O 9 (triangle or honeycomb) [13,18], Herbertsmithite (Kagome) [30][31][32] [35,36] (triangular biplanes), is the effect of vacancies at the magnetic sites. In minute amounts, these might simply give rise to an additional Curie term in the susceptibility and a Schottky like contribution to the heat capacity, keeping the correlated ground state intact.…”

Section: Discussionmentioning

confidence: 99%

“…Catuneanu et al [17] [14] exhibit atomic site disorder. According to a recent theoretical proposal of Smerald et al [19] correlated lattice disorder along with delocalized orphan spins can promote a spin-orbital liquid phase, and this was suggested to be the case for Ba 3 CuSb 2 O 9 [13,18,20]. The recent theoretical interest to underline the basic physics behind the family of materials with formula Ba 3 MX 2 O 9 (M = Co, Ni, Cu, Ru, Ir and X = Sb, Ti), further motivates us to explore these materials in detail.…”

Section: Introductionmentioning

confidence: 99%

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Ba3MxTi3−xO9(M=Ir

et al. 2016

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We report the structural and magnetic properties of the 4d (M = Rh) based and 5d (M = Ir) based systems Ba 3 M x Ti 3−x O 9 (nominally x = 0.5, 1). The studied compositions were found to crystallize in a hexagonal structure with the centrosymmetric space group P 6 3 /mmc. The structures comprise of A 2 O 9 polyhedra [with the A site (possibly) statistically occupied by M and Ti] in which pairs of transition metal ions are stacked along the crystallographic c axis. These pairs form triangular bilayers in the ab plane. The magnetic Rh and Ir ions occupy these bilayers, diluted by Ti ions even for x = 1. These bilayers are separated by a triangular layer which is dominantly occupied by Ti ions. From magnetization measurements we infer strong antiferromagnetic couplings for all of the materials but the absence of any spin-freezing or spin-ordering down to 2 K. Further, specific heat measurements down to 0.35 K show no sign of a phase transition for any of the compounds. Based on these thermodynamic measurements we propose the emergence of a quantum spin liquid ground state for Ba 3 Rh 0.5 Ti 2.5 O 9 , and Ba 3 Ir 0.5 Ti 2.5 O 9 , in addition to the already reported Ba 3 IrTi 2 O 9 .

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Ba3MxTi3−xO9(M=Ir

et al. 2016

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“…1A (12), sharply contradicting the previously reported crystal structure with a triangular lattice of Cu 2+ (13). In addition to the confirmation of a dynamic spin state down to 20 mK by muon spin spectroscopy (12,14,15), powder X-ray diffraction clearly indicates that even at low temperature, the hexagonal components remain, along with some orthorhombically distorted components. In the hexagonal phase, threefold symmetry exists for the Cu 2+ sites, which are surrounded by octahedrally coordinated oxygen, indicating the absence of a cooperative JT distortion.…”

mentioning

confidence: 99%

Absence of Jahn−Teller transition in the hexagonal Ba ₃ CuSb ₂ O ₉ single crystal

Katayama

Kimura

Han

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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With decreasing temperature, liquids generally freeze into a solid state, losing entropy in the process. However, exceptions to this trend exist, such as quantum liquids, which may remain unfrozen down to absolute zero owing to strong quantum entanglement effects that stabilize a disordered state with zero entropy. Examples of such liquids include Bose−Einstein condensation of cold atoms, superconductivity, quantum Hall state of electron systems, and quantum spin liquid state in the frustrated magnets. Moreover, recent studies have clarified the possibility of another exotic quantum liquid state based on the spin-orbital entanglement in FeSc 2 S 4 . To confirm this exotic ground state, experiments based on single-crystalline samples are essential. However, no such single-crystal study has been reported to date. Here, we report, to our knowledge, the first single-crystal study on the spin-orbital liquid candidate, 6H-Ba 3 CuSb 2 O 9 , and we have confirmed the absence of an orbital frozen state. In strongly correlated electron systems, orbital ordering usually appears at high temperatures in a process accompanied by a lattice deformation, called a static Jahn−Teller distortion. By combining synchrotron X-ray diffraction, electron spin resonance, Raman spectroscopy, and ultrasound measurements, we find that the static Jahn−Teller distortion is absent in the present material, which indicates that orbital ordering is suppressed down to the lowest temperatures measured. We discuss how such an unusual feature is realized with the help of spin degree of freedom, leading to a spin-orbital entangled quantum liquid state.Q uantum spin liquids have been widely recognized as a new state of matter, as an increasing number of candidates with quantum spin S = 1/2 have been found recently (1-4), a long time after the first proposal was made for the resonating valence-bond state (5). On the other hand, quantum liquids based on another electronic degree of freedom, orbital, have been theoretically proposed (6). However, this type of liquid state has never been experimentally confirmed because the energy of orbital correlation is normally one order of magnitude stronger than spin exchange coupling, leading to an orbital ordering at a significantly high temperature accompanied by a cooperative Jahn-Teller (JT) distortion. Nevertheless, if we can bring down the orbital energy to the same scale as for the spin coupling, it may lead to a novel spin-orbital entangled state, a "quantum spin-orbital liquid." A possible spin-orbital entangled liquid state with dimer correlations has been theoretically discussed on a triangular lattice with singly occupied but triply degenerate t 2g orbitals (7). In comparison with the t 2g orbitals' case, the experimental realization of such a quantum spin-orbital liquid state in the e g orbital system has been even more challenging (8), because e g orbitals more strongly couple to the JT modes.Perovskite-type 6H-Ba 3 CuSb 2 O 9 is a good candidate material for the spin-orbital liquid state that has been ...

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“…As shown in Figure 6g, the experimental results are well described by the singlet‐to‐triplet excitations of spin dimers, involving nearest and the next nearest neighbor interactions23, 24: I ( Q ) = ∣ F ( Q )∣ 2 Σ

m_{i}^{2}

[1 ‐ sin( Qd i )/( Qd i )], where

m_{i}^{2}

is the squared moment per formula unit and d i is distance between nearest or next nearest neighbor. Simple inclusion of the nearest neighbor interaction does not fit the data well 24, 25. The estimated values of

m_{i}^{2}

and d i at T = 80 mK are:

m_{1}^{2}

= 0.367

μ_{normalB}^{2}

, d 1 = 3.85 Å,

m_{2}^{2}

= 0.15

μ_{normalB}^{2}

and d 2 = 5.4 Å.…”

Section: Inelastic Neutron Scattering Measurementsmentioning

confidence: 88%

Quantum Magnetic Properties in Perovskite with Anderson Localized Artificial Spin‐1/2

et al. 2018

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Quantum magnetic properties in a geometrically frustrated lattice of spin‐1/2 magnet, such as quantum spin liquid or solid and the associated spin fractionalization, are considered key in developing a new phase of matter. The feasibility of observing the quantum magnetic properties, usually found in geometrically frustrated lattice of spin‐1/2 magnet, in a perovskite material with controlled disorder is demonstrated. It is found that the controlled chemical disorder, due to the chemical substitution of Ru ions by Co‐ions, in a simple perovskite CaRuO3 creates a random prototype configuration of artificial spin‐1/2 that forms dimer pairs between the nearest and further away ions. The localization of the Co impurity in the Ru matrix is analyzed using the Anderson localization formulation. The dimers of artificial spin‐1/2, due to the localization of Co impurities, exhibit singlet‐to‐triplet excitation at low temperature without any ordered spin correlation. The localized gapped excitation evolves into a gapless quasi‐continuum as dimer pairs break and create freely fluctuating fractionalized spins at high temperature. Together, these properties hint at a new quantum magnetic state with strong resemblance to the resonance valence bond system.

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Spin-Orbital Short-Range Order on a Honeycomb-Based Lattice

Cited by 141 publications

References 35 publications

Ba3MxTi3−xO9(M=Ir

Ba3MxTi3−xO9(M=Ir

Absence of Jahn−Teller transition in the hexagonal Ba ₃ CuSb ₂ O ₉ single crystal

Quantum Magnetic Properties in Perovskite with Anderson Localized Artificial Spin‐1/2

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Spin-Orbital Short-Range Order on a Honeycomb-Based Lattice

Cited by 141 publications

References 35 publications

Ba3MxTi3−xO9(M=Ir

Ba3MxTi3−xO9(M=Ir

Absence of Jahn−Teller transition in the hexagonal Ba 3 CuSb 2 O 9 single crystal

Quantum Magnetic Properties in Perovskite with Anderson Localized Artificial Spin‐1/2

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Absence of Jahn−Teller transition in the hexagonal Ba ₃ CuSb ₂ O ₉ single crystal