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Kundu S, Shahee A, Chakraborty A, Ranjith KM, Koo B, Sichelschmidt J, Telling MTF, Biswas PK, Baenitz M, Dasgupta I, Pujari S, Mahajan AV. Gapless Quantum Spin Liquid in the Triangular System Sr_{3}CuSb_{2}O_{9}. PHYSICAL REVIEW LETTERS 2020; 125:267202. [PMID: 33449718 DOI: 10.1103/physrevlett.125.267202] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2020] [Accepted: 12/01/2020] [Indexed: 06/12/2023]
Abstract
We report gapless quantum spin liquid behavior in the layered triangular Sr_{3}CuSb_{2}O_{9} system. X-ray diffraction shows superlattice reflections associated with atomic site ordering into triangular Cu planes well separated by Sb planes. Muon spin relaxation measurements show that the S=1/2 moments at the magnetically active Cu sites remain dynamic down to 65 mK in spite of a large antiferromagnetic exchange scale evidenced by a large Curie-Weiss temperature θ_{CW}≃-143 K as extracted from the bulk susceptibility. Specific heat measurements also show no sign of long-range order down to 0.35 K. The magnetic specific heat (C_{m}) below 5 K reveals a C_{m}=γT+αT^{2} behavior. The significant T^{2} contribution to the magnetic specific heat invites a phenomenology in terms of the so-called Dirac spinon excitations with a linear dispersion. From the low-T specific heat data, we estimate the dominant exchange scale to be ∼36 K using a Dirac spin liquid ansatz which is not far from the values inferred from microscopic density functional theory calculations (∼45 K) as well as high-temperature susceptibility analysis (∼70 K). The linear specific heat coefficient is about 18 mJ/mol K^{2} which is somewhat larger than for typical Fermi liquids.
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Affiliation(s)
- S Kundu
- Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
| | - Aga Shahee
- Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
| | - Atasi Chakraborty
- School of Physical Sciences, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
| | - K M Ranjith
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
| | - B Koo
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
| | - Jörg Sichelschmidt
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
| | - Mark T F Telling
- ISIS Pulsed Neutron and Muon Source, STFC Rutherford Appleton Laboratory, Harwell Campus, Didcot, Oxfordshire OX110QX, United Kingdom
| | - P K Biswas
- ISIS Pulsed Neutron and Muon Source, STFC Rutherford Appleton Laboratory, Harwell Campus, Didcot, Oxfordshire OX110QX, United Kingdom
| | - M Baenitz
- Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany
| | - I Dasgupta
- School of Physical Sciences, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
| | - Sumiran Pujari
- Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
| | - A V Mahajan
- Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
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Man H, Halim M, Sawa H, Hagiwara M, Wakabayashi Y, Nakatsuji S. Spin-orbital entangled liquid state in the copper oxide Ba 3CuSb 2O 9. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2018; 30:443002. [PMID: 30210058 DOI: 10.1088/1361-648x/aae106] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Structure with orbital degeneracy is unstable toward spontaneous distortion. Such orbital correlation usually has a much higher energy scale than spins, and therefore, magnetic transition takes place at a much lower temperature, almost independently from orbital ordering. However, when the energy scales of orbitals and spins meet, there is a possibility of spin-orbital entanglement that would stabilize novel ground state such as spin-orbital liquid and random singlet state. Here we review on such a novel spin-orbital magnetism found in the hexagonal perovskite oxide Ba3CuSb2O9, which hosts a self-organized honeycomblike short-range order of a strong Jahn-Teller ion Cu2+. Comprehensive structural and magnetic measurements have revealed that the system has neither magnetic nor Jahn-Teller transition down to the lowest temperatures, and Cu spins and orbitals retain the hexagonal symmetry and paramagnetic state. Various macroscopic and microscopic measurements all indicate that spins and orbitals remain fluctuating down to low temperatures without freezing, forming a spin-orbital entangled liquid state.
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Affiliation(s)
- Huiyuan Man
- Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
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Li J, Jiang P, Gao W, Cong R, Yang T. Chemical Substitution-Induced and Competitive Formation of 6H and 3C Perovskite Structures in Ba3–xSrxZnSb2O9: The Coexistence of Two Perovskites in 0.3 ≤ x ≤ 1.0. Inorg Chem 2017; 56:14335-14344. [DOI: 10.1021/acs.inorgchem.7b02429] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Jing Li
- College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 401331, P. R. China
| | - Pengfei Jiang
- College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 401331, P. R. China
| | - Wenliang Gao
- College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 401331, P. R. China
| | - Rihong Cong
- College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 401331, P. R. China
| | - Tao Yang
- College of Chemistry and Chemical Engineering, Chongqing University, Chongqing 401331, P. R. China
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Sugii K, Shimozawa M, Watanabe D, Suzuki Y, Halim M, Kimata M, Matsumoto Y, Nakatsuji S, Yamashita M. Thermal Hall Effect in a Phonon-Glass Ba_{3}CuSb_{2}O_{9}. PHYSICAL REVIEW LETTERS 2017; 118:145902. [PMID: 28430491 DOI: 10.1103/physrevlett.118.145902] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2016] [Indexed: 06/07/2023]
Abstract
A distinct thermal Hall signal is observed in a quantum spin liquid candidate Ba_{3}CuSb_{2}O_{9}. The transverse thermal conductivity shows a power-law temperature dependence below 50 K, where a spin gap opens. We suggest that because of the very low longitudinal thermal conductivity and the thermal Hall signals, a phonon Hall effect is induced by strong phonon scattering of orphan Cu^{2+} spins formed in the random domains of the Cu^{2+}-Sb^{5+} dumbbells in Ba_{3}CuSb_{2}O_{9}.
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Affiliation(s)
- K Sugii
- The Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan
| | - M Shimozawa
- The Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan
| | - D Watanabe
- The Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan
| | - Y Suzuki
- The Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan
| | - M Halim
- The Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan
| | - M Kimata
- The Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan
| | - Y Matsumoto
- The Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan
| | - S Nakatsuji
- The Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan
| | - M Yamashita
- The Institute for Solid State Physics, The University of Tokyo, Kashiwa 277-8581, Japan
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Abstract
Recent studies highlighting the importance of diffuse scattering for materials science are presented.
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Affiliation(s)
- Hiroshi Sawa
- Department of Applied Physics, School of Engineering, Nagoya University, Nagoya, Aichi, Japan
- Correspondence e-mail:
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Designing Quantum Spin-Orbital Liquids in Artificial Mott Insulators. Sci Rep 2016; 6:31737. [PMID: 27553516 PMCID: PMC4995463 DOI: 10.1038/srep31737] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2016] [Accepted: 07/25/2016] [Indexed: 11/10/2022] Open
Abstract
Quantum spin-orbital liquids are elusive strongly correlated states of matter that emerge from quantum frustration between spin and orbital degrees of freedom. A promising route towards the observation of those states is the creation of artificial Mott insulators where antiferromagnetic correlations between spins and orbitals can be designed. We show that Coulomb impurity lattices on the surface of gapped honeycomb substrates, such as graphene on SiC, can be used to simulate SU(4) symmetric spin-orbital lattice models. We exploit the property that massive Dirac fermions form mid-gap bound states with spin and valley degeneracies in the vicinity of a Coulomb impurity. Due to electronic repulsion, the antiferromagnetic correlations of the impurity lattice are driven by a super-exchange interaction with SU(4) symmetry, which emerges from the bound states degeneracy at quarter filling. We propose that quantum spin-orbital liquids can be engineered in artificially designed solid-state systems at vastly higher temperatures than achievable in optical lattices with cold atoms. We discuss the experimental setup and possible scenarios for candidate quantum spin-liquids in Coulomb impurity lattices of various geometries.
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Smerald A, Mila F. Disorder-Driven Spin-Orbital Liquid Behavior in the Ba3XSb2O9 Materials. PHYSICAL REVIEW LETTERS 2015; 115:147202. [PMID: 26551821 DOI: 10.1103/physrevlett.115.147202] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2015] [Indexed: 06/05/2023]
Abstract
Recent experiments on the Ba(3)XSb(2)O(9) family have revealed materials that potentially realize spin- and spin-orbital liquid physics. However, the lattice structure of these materials is complicated due to the presence of charged X(2+)-Sb(5+) dumbbells, with two possible orientations. To model the lattice structure, we consider a frustrated model of charged dumbbells on the triangular lattice, with long-range Coulomb interactions. We study this model using Monte Carlo simulation, and find a freezing temperature, T(frz), at which the simulated structure factor matches well to low-temperature x-ray diffraction data for Ba(3)CuSb(2)O(9). At T=T(frz) we find a complicated "branching" structure of superexchange-linked X(2+) clusters, which form a fractal pattern with fractal dimension d(f)=1.90. We show that this gives a natural explanation for the presence of orphan spins. Finally we provide a plausible mechanism by which such dumbbell disorder can promote a spin-orbital resonant state with delocalized orphan spins.
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Affiliation(s)
- Andrew Smerald
- Institut de Théorie des Phénomènes Physiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
| | - Frédéric Mila
- Institut de Théorie des Phénomènes Physiques, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
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Absence of Jahn-Teller transition in the hexagonal Ba3CuSb2O9 single crystal. Proc Natl Acad Sci U S A 2015; 112:9305-9. [PMID: 26170280 DOI: 10.1073/pnas.1508941112] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
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 FeSc2S4. 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-Ba3CuSb2O9, 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.
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