51
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A spin–orbital-entangled quantum liquid on a honeycomb lattice. Nature 2018; 554:341-345. [DOI: 10.1038/nature25482] [Citation(s) in RCA: 217] [Impact Index Per Article: 36.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2017] [Accepted: 12/04/2017] [Indexed: 11/08/2022]
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52
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Yu YJ, Xu Y, Ran KJ, Ni JM, Huang YY, Wang JH, Wen JS, Li SY. Ultralow-Temperature Thermal Conductivity of the Kitaev Honeycomb Magnet α-RuCl_{3} across the Field-Induced Phase Transition. PHYSICAL REVIEW LETTERS 2018; 120:067202. [PMID: 29481222 DOI: 10.1103/physrevlett.120.067202] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2017] [Indexed: 06/08/2023]
Abstract
Recently, there have been increasingly hot debates on whether there exists a quantum spin liquid in the Kitaev honeycomb magnet α-RuCl_{3} in a high magnetic field. To investigate this issue, we perform ultralow-temperature thermal conductivity measurements on single crystals of α-RuCl_{3} down to 80 mK and up to 9 T. Our experiments clearly show a field-induced phase transition occurring at μ_{0}H_{c}≈7.5 T, above which the magnetic order is completely suppressed. The minimum of thermal conductivity at 7.5 T is attributed to the strong scattering of phonons by magnetic fluctuations. Most importantly, above 7.5 T, we do not observe any significant contribution of thermal conductivity from gapless magnetic excitations, which puts a strong constraint on the nature of the high-field phase of α-RuCl_{3}.
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Affiliation(s)
- Y J Yu
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China
| | - Y Xu
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China
| | - K J Ran
- National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
| | - J M Ni
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China
| | - Y Y Huang
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China
| | - J H Wang
- National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
| | - J S Wen
- National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - S Y Li
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
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53
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Furukawa T, Kobashi K, Kurosaki Y, Miyagawa K, Kanoda K. Quasi-continuous transition from a Fermi liquid to a spin liquid in κ-(ET) 2Cu 2(CN) 3. Nat Commun 2018; 9:307. [PMID: 29358740 PMCID: PMC5778024 DOI: 10.1038/s41467-017-02679-7] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2017] [Accepted: 12/18/2017] [Indexed: 11/10/2022] Open
Abstract
The Mott metal-insulator transition—a manifestation of Coulomb interactions among electrons—is known as a discontinuous transition. Recent theoretical studies, however, suggest that the transition is continuous if the Mott insulator carries a spin liquid with a spinon Fermi surface. Here, we demonstrate the case of a quasi-continuous Mott transition from a Fermi liquid to a spin liquid in an organic triangular-lattice system κ-(ET)2Cu2(CN)3. Transport experiments performed under fine pressure tuning have found that as the Mott transition is approached, the Fermi liquid coherence temperature continuously falls to the scale of kelvins, with a divergent quasi-particle decay rate on the metal side, and the charge gap continuously closes on the insulator side. A Clausius-Clapeyron analysis provides thermodynamic evidence for the extremely weak first-order nature of the transition. These results provide additional support for the existence of a spinon Fermi surface, which becomes an electron Fermi surface when charges are delocalized. Several organic materials exhibit spin liquid phases, which are predicted to host exotic spinon excitations that emerge from non-local quantum effects. Here, the authors identify a quasi-continuous phase transition in κ-(ET)2Cu2(CN)3 that may be associated with the presence of spinons.
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Affiliation(s)
- Tetsuya Furukawa
- Department of Applied Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan. .,Department of Applied Physics, Tokyo University of Science, Niijyuku 6-3-1, Katsushika-ku, Tokyo, 125-8585, Japan.
| | - Kazuhiko Kobashi
- Department of Applied Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan
| | - Yosuke Kurosaki
- Department of Applied Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan
| | - Kazuya Miyagawa
- Department of Applied Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan
| | - Kazushi Kanoda
- Department of Applied Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan.
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54
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Tanatar MA, Bondarenko VA, Timmons EI, Prozorov R. Modular portable unit for thermal conductivity measurements in multiple cryogenic/magnetic field environments. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2018; 89:013903. [PMID: 29390721 DOI: 10.1063/1.5001708] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
A modular design for a miniature thermal conductivity cell suitable for a dilution refrigerator and other sample-in-vacuum cryogenic environments with different magnet options is described. The sample is mounted once and the contacts remain in place when the unit is repositioned or transported between different magnets and cryostats. This mobility enables comprehensive measurements with access to specific options, such as vector magnet in one lab and ultra-high field in another. This design enables significant expansion of the temperature range by using not only dilution refrigerators but also 3He, 4He cryostats and even ubiquitous Quantum Design Physical Property Measurement System.
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Affiliation(s)
- M A Tanatar
- Ames Laboratory US DOE, Ames, Iowa 50011, USA
| | | | - E I Timmons
- Ames Laboratory US DOE, Ames, Iowa 50011, USA
| | - R Prozorov
- Ames Laboratory US DOE, Ames, Iowa 50011, USA
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55
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Zhang B, Baker PJ, Zhang Y, Wang D, Wang Z, Su S, Zhu D, Pratt FL. Quantum Spin Liquid from a Three-Dimensional Copper-Oxalate Framework. J Am Chem Soc 2017; 140:122-125. [DOI: 10.1021/jacs.7b11179] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Bin Zhang
- Organic Solid Laboratory, CAS Research/Education Center for Excellence in Molecular Sciences, CMS & BNLMS, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
| | - Peter J. Baker
- ISIS
Pulsed Neutron and Muon Source, STFC Rutherford Appleton Laboratory, Didcot OX11 0QX, United Kingdom
| | - Yan Zhang
- Institute
of Condensed Matter and Material Physics, Department of Physics, Peking University, Beijing 100871, People’s Republic of China
| | - Dongwei Wang
- CAS
Key Laboratory of Standardization and Measurement for Nanotechnology, National Center for Nanoscience and Technology, Beijing 100190, People’s Republic of China
| | - Zheming Wang
- State
Key Laboratory of Rare Earth Materials Chemistry and Applications,
BNLMS, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, People’s Republic of China
| | - Shaokui Su
- Beijing National
Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
| | - Daoben Zhu
- Organic Solid Laboratory, CAS Research/Education Center for Excellence in Molecular Sciences, CMS & BNLMS, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s Republic of China
| | - Francis L. Pratt
- ISIS
Pulsed Neutron and Muon Source, STFC Rutherford Appleton Laboratory, Didcot OX11 0QX, United Kingdom
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56
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Shimozawa M, Hashimoto K, Ueda A, Suzuki Y, Sugii K, Yamada S, Imai Y, Kobayashi R, Itoh K, Iguchi S, Naka M, Ishihara S, Mori H, Sasaki T, Yamashita M. Quantum-disordered state of magnetic and electric dipoles in an organic Mott system. Nat Commun 2017; 8:1821. [PMID: 29180819 PMCID: PMC5703743 DOI: 10.1038/s41467-017-01849-x] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2017] [Accepted: 10/18/2017] [Indexed: 11/24/2022] Open
Abstract
Strongly enhanced quantum fluctuations often lead to a rich variety of quantum-disordered states. Developing approaches to enhance quantum fluctuations may open paths to realize even more fascinating quantum states. Here, we demonstrate that a coupling of localized spins with the zero-point motion of hydrogen atoms, that is, proton fluctuations in a hydrogen-bonded organic Mott insulator provides a different class of quantum spin liquids (QSLs). We find that divergent dielectric behavior associated with the approach to hydrogen-bond order is suppressed by the quantum proton fluctuations, resulting in a quantum paraelectric (QPE) state. Furthermore, our thermal-transport measurements reveal that a QSL state with gapless spin excitations rapidly emerges upon entering the QPE state. These findings indicate that the quantum proton fluctuations give rise to a QSL—a quantum-disordered state of magnetic and electric dipoles—through the coupling between the electron and proton degrees of freedom. The organic material κ-H3(Cat-EDT-TTF)2 has been suggested to exhibit a quantum spin liquid phase in which quantum fluctuations prevent the formation of magnetic order. Here, the authors show that this may be a result of fluctuations of hydrogen atoms, rather than more conventional geometric frustration.
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Affiliation(s)
- M Shimozawa
- The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba, 277-8581, Japan.
| | - K Hashimoto
- Institute for Materials Research, Tohoku University, Aoba-ku, Sendai, 980-8577, Japan.
| | - A Ueda
- The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba, 277-8581, Japan
| | - Y Suzuki
- The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba, 277-8581, Japan
| | - K Sugii
- The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba, 277-8581, Japan
| | - S Yamada
- The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba, 277-8581, Japan
| | - Y Imai
- The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba, 277-8581, Japan
| | - R Kobayashi
- Institute for Materials Research, Tohoku University, Aoba-ku, Sendai, 980-8577, Japan
| | - K Itoh
- Institute for Materials Research, Tohoku University, Aoba-ku, Sendai, 980-8577, Japan
| | - S Iguchi
- Institute for Materials Research, Tohoku University, Aoba-ku, Sendai, 980-8577, Japan
| | - M Naka
- Department of Physics, Tohoku University, Sendai, 980-8578, Japan.,Waseda Institute for Advanced Study, Waseda University, Shinjuku, Tokyo, 169-8050, Japan
| | - S Ishihara
- Department of Physics, Tohoku University, Sendai, 980-8578, Japan
| | - H Mori
- The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba, 277-8581, Japan
| | - T Sasaki
- Institute for Materials Research, Tohoku University, Aoba-ku, Sendai, 980-8577, Japan
| | - M Yamashita
- The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba, 277-8581, Japan
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57
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Dynamical time-reversal symmetry breaking and photo-induced chiral spin liquids in frustrated Mott insulators. Nat Commun 2017; 8:1192. [PMID: 29084937 PMCID: PMC5662750 DOI: 10.1038/s41467-017-00876-y] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2017] [Accepted: 08/01/2017] [Indexed: 11/23/2022] Open
Abstract
The search for quantum spin liquids in frustrated quantum magnets recently has enjoyed a surge of interest, with various candidate materials under intense scrutiny. However, an experimental confirmation of a gapped topological spin liquid remains an open question. Here, we show that circularly polarized light can provide a knob to drive frustrated Mott insulators into a chiral spin liquid, realizing an elusive quantum spin liquid with topological order. We find that the dynamics of a driven Kagome Mott insulator is well-captured by an effective Floquet spin model, with heating strongly suppressed, inducing a scalar spin chirality Si · (Sj × Sk) term which dynamically breaks time-reversal while preserving SU(2) spin symmetry. We fingerprint the transient phase diagram and find a stable photo-induced chiral spin liquid near the equilibrium state. The results presented suggest employing dynamical symmetry breaking to engineer quantum spin liquids and access elusive phase transitions that are not readily accessible in equilibrium. Exotic quantum phases like spin liquids have long been investigated theoretically but it is difficult to find materials that realize these states in equilibrium. Here the authors propose that optical driving could be used to induce chiral spin liquid behaviour in frustrated Mott insulators.
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58
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Yamamoto T, Fujimoto T, Naito T, Nakazawa Y, Tamura M, Yakushi K, Ikemoto Y, Moriwaki T, Kato R. Charge and Lattice Fluctuations in Molecule-Based Spin Liquids. Sci Rep 2017; 7:12930. [PMID: 29018228 PMCID: PMC5635065 DOI: 10.1038/s41598-017-13118-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2017] [Accepted: 09/19/2017] [Indexed: 11/10/2022] Open
Abstract
Spin liquid (SL) systems have been the subject of much attention recently, as they have been theoretically predicted to not freeze, even at 0 K. Despite extensive searches being made for such a system, only a few candidates have been found. All of these candidates share geometrical frustrations that are based on triangular lattices. We applied vibrational spectroscopy to one of the candidates of a molecule-based SL system, and we compared its results against three antiferromagnetic compounds and four charge-ordered compounds. All of their structural motifs belong to triangular lattices. The C=C stretching modes in the SL state indicated that there were charge and lattice fluctuations. These fluctuations were suppressed but non-negligible in the AF compounds. This finding is potentially significant, as it indicates that a hidden lattice and charge fluctuation are the driving force of a geometrical frustration, which eventually leads to a SL state.
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Affiliation(s)
- Takashi Yamamoto
- Graduate School of Science and Technology, Ehime University, 2-5 Bunkyo-cho, Matsuyama, 7908577, Japan. .,RIKEN, 2-1 Hirosawa, Wako, 3510198, Japan.
| | - Takashi Fujimoto
- Graduate School of Science and Technology, Ehime University, 2-5 Bunkyo-cho, Matsuyama, 7908577, Japan
| | - Toshio Naito
- Graduate School of Science and Technology, Ehime University, 2-5 Bunkyo-cho, Matsuyama, 7908577, Japan
| | - Yasuhiro Nakazawa
- Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka, 560-0043, Japan
| | - Masafumi Tamura
- Department of Physics, Faculty of Science and Technology, Tokyo University of Science, 2641 Yamazaki, Noda, 2788510, Japan
| | - Kyuya Yakushi
- Toyota Physical and Chemical Research Institute, 41-1 Yokomichi, Nagakute, 4801192, Japan
| | - Yuka Ikemoto
- JASRI, SPring-8, 1-1-1 Kouto, Sayo, Hyogo, 679-5198, Japan
| | - Taro Moriwaki
- JASRI, SPring-8, 1-1-1 Kouto, Sayo, Hyogo, 679-5198, Japan
| | - Reizo Kato
- RIKEN, 2-1 Hirosawa, Wako, 3510198, Japan
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59
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Nasu J, Yoshitake J, Motome Y. Thermal Transport in the Kitaev Model. PHYSICAL REVIEW LETTERS 2017; 119:127204. [PMID: 29341648 DOI: 10.1103/physrevlett.119.127204] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/30/2017] [Indexed: 06/07/2023]
Abstract
In conventional insulating magnets, heat is carried by magnons and phonons. In contrast, when the magnets harbor a quantum spin liquid state, emergent quasiparticles from the fractionalization of quantum spins can carry heat. Here, we investigate unconventional thermal transport yielded by such exotic carriers, in both longitudinal and transverse components, for the Kitaev model, whose ground state is exactly shown to be a quantum spin liquid with fractional excitations described as itinerant Majorana fermions and localized Z_{2} fluxes. We find that the longitudinal thermal conductivity exhibits a single peak at a high temperature, while the nonzero frequency component has a peak at a low temperature, reflecting the spin fractionalization. On the other hand, we show that the transverse thermal conductivity is induced by the magnetic field in a wide temperature range up to the energy scale of the bare exchange coupling; while increasing temperature, the transverse response divided by temperature decreases from the quantized value expected for the topologically nontrivial ground state and shows nonmonotonic temperature dependence. These characteristic behaviors provide experimentally accessible evidence of fractional excitations in the proximity to the Kitaev quantum spin liquid.
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Affiliation(s)
- Joji Nasu
- Department of Physics, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan
| | - Junki Yoshitake
- Department of Applied Physics, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
| | - Yukitoshi Motome
- Department of Applied Physics, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
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60
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61
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Itou T, Watanabe E, Maegawa S, Tajima A, Tajima N, Kubo K, Kato R, Kanoda K. Slow dynamics of electrons at a metal-Mott insulator boundary in an organic system with disorder. SCIENCE ADVANCES 2017; 3:e1601594. [PMID: 28819640 PMCID: PMC5553821 DOI: 10.1126/sciadv.1601594] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/12/2016] [Accepted: 07/06/2017] [Indexed: 06/07/2023]
Abstract
The Mott transition-a metal-insulator transition caused by repulsive Coulomb interactions between electrons-is a central issue in condensed matter physics because it is the mother earth of various attractive phenomena. Outstanding examples are high-Tc (critical temperature) cuprates and manganites exhibiting colossal magnetoresistance. Furthermore, spin liquid states, which are quantum-fluctuation-driven disordered ground states in antiferromagnets, have recently been found in magnetic systems very near the Mott transition. To date, intensive studies on the Mott transition have been conducted and appear to have established a nearly complete framework for understanding the Mott transition. We found an unknown type of Mott transition in an organic spin liquid material with a slightly disordered lattice. Around the Mott transition region of this material under pressure, nuclear magnetic resonance experiments capture the emergence of slow electronic fluctuations of the order of kilohertz or lower, which is not expected in the conventional Mott transition that appears as a clear first-order transition at low temperatures. We suggest that they are due to the unconventional metal-insulator fluctuations emerging around the disordered Mott transition in analogy to the slowly fluctuating spin phase, or Griffiths phase, realized in Ising spin systems with disordered lattices.
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Affiliation(s)
- Tetsuaki Itou
- Department of Applied Physics, Tokyo University of Science, Katsushika-ku, Tokyo 125-8585, Japan
- Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
| | - Eri Watanabe
- Graduate School of Human and Environmental Studies, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
| | - Satoru Maegawa
- Graduate School of Human and Environmental Studies, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
| | - Akiko Tajima
- Condensed Molecular Materials Laboratory, RIKEN, Wako-shi, Saitama 351-0198, Japan
| | - Naoya Tajima
- Condensed Molecular Materials Laboratory, RIKEN, Wako-shi, Saitama 351-0198, Japan
- Department of Physics, Toho University, Funabashi-shi, Chiba 274-8510, Japan
| | - Kazuya Kubo
- Condensed Molecular Materials Laboratory, RIKEN, Wako-shi, Saitama 351-0198, Japan
- Research Institute for Electronic Science, Hokkaido University, Kita-ku, Sapporo 001-0020, Japan
| | - Reizo Kato
- Condensed Molecular Materials Laboratory, RIKEN, Wako-shi, Saitama 351-0198, Japan
| | - Kazushi Kanoda
- Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
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62
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Baek SH, Do SH, Choi KY, Kwon YS, Wolter AUB, Nishimoto S, van den Brink J, Büchner B. Evidence for a Field-Induced Quantum Spin Liquid in α-RuCl_{3}. PHYSICAL REVIEW LETTERS 2017; 119:037201. [PMID: 28777603 DOI: 10.1103/physrevlett.119.037201] [Citation(s) in RCA: 66] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2017] [Indexed: 06/07/2023]
Abstract
We report a ^{35}Cl nuclear magnetic resonance study in the honeycomb lattice α-RuCl_{3}, a material that has been suggested to potentially realize a Kitaev quantum spin liquid (QSL) ground state. Our results provide direct evidence that α-RuCl_{3} exhibits a magnetic-field-induced QSL. For fields larger than ∼10 T, a spin gap opens up while resonance lines remain sharp, evidencing that spins are quantum disordered and locally fluctuating. The spin gap increases linearly with an increasing magnetic field, reaching ∼50 K at 15 T, and is nearly isotropic with respect to the field direction. The unusual rapid increase of the spin gap with increasing field and its isotropic nature are incompatible with conventional magnetic ordering and, in particular, exclude that the ground state is a fully polarized ferromagnet. The presence of such a field-induced gapped QSL phase has indeed been predicted in the Kitaev model.
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Affiliation(s)
- S-H Baek
- IFW Dresden, Helmholtzstr. 20, 01069 Dresden, Germany
| | - S-H Do
- Department of Physics, Chung-Ang University, Seoul 156-756, Republic of Korea
| | - K-Y Choi
- Department of Physics, Chung-Ang University, Seoul 156-756, Republic of Korea
| | - Y S Kwon
- Department of Emerging Materials Science, DGIST, Daegu 711-873, Republic of Korea
| | - A U B Wolter
- IFW Dresden, Helmholtzstr. 20, 01069 Dresden, Germany
| | - S Nishimoto
- IFW Dresden, Helmholtzstr. 20, 01069 Dresden, Germany
- Department of Physics, Technische Universität Dresden, 01062 Dresden, Germany
| | - Jeroen van den Brink
- IFW Dresden, Helmholtzstr. 20, 01069 Dresden, Germany
- Department of Physics, Technische Universität Dresden, 01062 Dresden, Germany
| | - B Büchner
- IFW Dresden, Helmholtzstr. 20, 01069 Dresden, Germany
- Department of Physics, Technische Universität Dresden, 01062 Dresden, Germany
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63
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Abstract
1T-TaS2 is unique among transition metal dichalcogenides in that it is understood to be a correlation-driven insulator, where the unpaired electron in a 13-site cluster experiences enough correlation to form a Mott insulator. We argue, based on existing data, that this well-known material should be considered as a quantum spin liquid, either a fully gapped [Formula: see text] spin liquid or a Dirac spin liquid. We discuss the exotic states that emerge upon doping and propose further experimental probes.
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Affiliation(s)
- K T Law
- Department of Physics, Hong Kong University of Science and Technology, Hong Kong, China
| | - Patrick A Lee
- Department of Physics, Massachusetts Institute of Technology, Cambridge MA 02139
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64
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Leahy IA, Pocs CA, Siegfried PE, Graf D, Do SH, Choi KY, Normand B, Lee M. Anomalous Thermal Conductivity and Magnetic Torque Response in the Honeycomb Magnet α-RuCl_{3}. PHYSICAL REVIEW LETTERS 2017; 118:187203. [PMID: 28524686 DOI: 10.1103/physrevlett.118.187203] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2016] [Indexed: 06/07/2023]
Abstract
We report on the unusual behavior of the in-plane thermal conductivity κ and torque τ response in the Kitaev-Heisenberg material α-RuCl_{3}. κ shows a striking enhancement with linear growth beyond H=7 T, where magnetic order disappears, while τ for both of the in-plane symmetry directions shows an anomaly at the same field. The temperature and field dependence of κ are far more complex than conventional phonon and magnon contributions, and require us to invoke the presence of unconventional spin excitations whose properties are characteristic of a field-induced spin-liquid phase related to the enigmatic physics of the Kitaev model in an applied magnetic field.
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Affiliation(s)
- Ian A Leahy
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
| | - Christopher A Pocs
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
| | - Peter E Siegfried
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
| | - David Graf
- National High Magnetic Field Laboratory, Tallahassee, Florida 32310, USA
| | - S-H Do
- Department of Physics, Chung-Ang University, Seoul 790-784, South Korea
| | - Kwang-Yong Choi
- Department of Physics, Chung-Ang University, Seoul 790-784, South Korea
| | - B Normand
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
| | - Minhyea Lee
- Department of Physics, University of Colorado, Boulder, Colorado 80309, USA
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65
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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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Nasu J, Kato Y, Yoshitake J, Kamiya Y, Motome Y. Spin-Liquid-to-Spin-Liquid Transition in Kitaev Magnets Driven by Fractionalization. PHYSICAL REVIEW LETTERS 2017; 118:137203. [PMID: 28409982 DOI: 10.1103/physrevlett.118.137203] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2016] [Indexed: 06/07/2023]
Abstract
While phase transitions between magnetic analogs of the three states of matter-a long-range ordered state, paramagnet, and spin liquid-are extensively studied, the possibility of "liquid-liquid" transitions, namely, between different spin liquids, remains elusive. By introducing the additional Ising coupling into the honeycomb Kitaev model with bond asymmetry, we discover that the Kitaev spin liquid turns into a spin-nematic quantum paramagnet before a magnetic order is established by the Ising coupling. The quantum phase transition between the two liquid states accompanies a topological change driven by fractionalized excitations, the Z_{2} gauge fluxes, and is of first order. At finite temperatures, this yields a persisting first-order transition line that terminates at a critical point located deep inside the regime where quantum spins are fractionalized. It is suggested that similar transitions may occur in other perturbed Kitaev magnets with bond asymmetry.
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Affiliation(s)
- Joji Nasu
- Department of Physics, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan
| | - Yasuyuki Kato
- Department of Applied Physics, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
| | - Junki Yoshitake
- Department of Applied Physics, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
| | - Yoshitomo Kamiya
- Condensed Matter Theory Laboratory, RIKEN, Wako, Saitama 351-0198, Japan
| | - Yukitoshi Motome
- Department of Applied Physics, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan
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67
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Ranjith KM, Brinda K, Arjun U, Hegde NG, Nath R. Double phase transition in the triangular antiferromagnet Ba 3CoTa 2O 9. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2017; 29:115804. [PMID: 28067634 DOI: 10.1088/1361-648x/aa57be] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Here, we report the synthesis and magnetic properties of a new triangular lattice antiferromagnet Ba3CoTa2O9. The effective spin of Co2+ is found to be J = 1/2 at low temperatures due to the combined effect of crystal field and spin-orbit coupling. Ba3CoTa2O9 undergoes two successive magnetic phase transitions at [Formula: see text] K and [Formula: see text] K in zero applied field, which is typical for triangular antiferromagnets with the easy-axis magnetic anisotropy. With increasing field, the transition anomalies are found to shift toward low temperatures, confirming the antiferromagnetic nature of the transitions. At higher fields, the transition peaks in the heat capacity data disappear and give way to a broad maximum, which can be ascribed to a Schottky anomaly due to the Zeeman splitting of spin levels. The H - T phase diagram of the compound shows three distinct phases. The possible nature of these phases is discussed.
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Affiliation(s)
- K M Ranjith
- School of Physics, Indian Institute of Science Education and Research Thiruvananthapuram-695016, India
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68
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Savary L, Balents L. Disorder-Induced Quantum Spin Liquid in Spin Ice Pyrochlores. PHYSICAL REVIEW LETTERS 2017; 118:087203. [PMID: 28282206 DOI: 10.1103/physrevlett.118.087203] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Indexed: 06/06/2023]
Abstract
We propose that in a certain class of magnetic materials, known as non-Kramers "spin ice," disorder induces quantum entanglement. Instead of driving glassy behavior, disorder provokes quantum superpositions of spins throughout the system and engenders an associated emergent gauge structure and set of fractional excitations. More precisely, disorder transforms a classical phase governed by a large entropy, classical spin ice, into a quantum spin liquid governed by entanglement. As the degree of disorder is increased, the system transitions between (i) a "regular" Coulombic spin liquid, (ii) a phase known as "Mott glass," which contains rare gapless regions in real space, but whose behavior on long length scales is only modified quantitatively, and (iii) a true glassy phase for random distributions with large width or large mean amplitude.
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Affiliation(s)
- Lucile Savary
- Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA
| | - Leon Balents
- Kavli Institute for Theoretical Physics, University of California, Santa Barbara, California 93106-4030, USA
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69
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Savary L, Balents L. Quantum spin liquids: a review. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2017; 80:016502. [PMID: 27823986 DOI: 10.1088/0034-4885/80/1/016502] [Citation(s) in RCA: 296] [Impact Index Per Article: 42.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Quantum spin liquids may be considered 'quantum disordered' ground states of spin systems, in which zero-point fluctuations are so strong that they prevent conventional magnetic long-range order. More interestingly, quantum spin liquids are prototypical examples of ground states with massive many-body entanglement, which is of a degree sufficient to render these states distinct phases of matter. Their highly entangled nature imbues quantum spin liquids with unique physical aspects, such as non-local excitations, topological properties, and more. In this review, we discuss the nature of such phases and their properties based on paradigmatic models and general arguments, and introduce theoretical technology such as gauge theory and partons, which are conveniently used in the study of quantum spin liquids. An overview is given of the different types of quantum spin liquids and the models and theories used to describe them. We also provide a guide to the current status of experiments in relation to study quantum spin liquids, and to the diverse probes used therein.
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Affiliation(s)
- Lucile Savary
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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70
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Xu Y, Zhang J, Li YS, Yu YJ, Hong XC, Zhang QM, Li SY. Absence of Magnetic Thermal Conductivity in the Quantum Spin-Liquid Candidate YbMgGaO_{4}. PHYSICAL REVIEW LETTERS 2016; 117:267202. [PMID: 28059548 DOI: 10.1103/physrevlett.117.267202] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2016] [Indexed: 06/06/2023]
Abstract
We present the ultralow-temperature specific heat and thermal conductivity measurements on single crystals of YbMgGaO_{4}, which was recently argued to be a promising candidate for a quantum spin liquid (QSL). In a zero magnetic field, a large magnetic contribution of specific heat is observed, and exhibits a power-law temperature dependence (C_{m}∼T^{0.74}). On the contrary, we do not observe any significant contribution of thermal conductivity from magnetic excitations. In magnetic fields H≥6 T, the exponential T dependence of C_{m} and the enhanced thermal conductivity indicate a magnon gap of the fully polarized state. The absence of magnetic thermal conductivity at the zero field in this QSL candidate puts a strong constraint on the theories of its ground state.
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Affiliation(s)
- Y Xu
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China
| | - J Zhang
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China
| | - Y S Li
- Department of Physics, Renmin University of China, Beijing 100872, China
- Experimental Physics VI, Center for Electronic Correlations and Magnetism, University of Augsburg, 86159 Augsburg, Germany
| | - Y J Yu
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China
| | - X C Hong
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China
| | - Q M Zhang
- Department of Physics, Renmin University of China, Beijing 100872, China
- Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
| | - S Y Li
- State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China
- Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China
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71
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Yadav R, Bogdanov NA, Katukuri VM, Nishimoto S, van den Brink J, Hozoi L. Kitaev exchange and field-induced quantum spin-liquid states in honeycomb α-RuCl 3. Sci Rep 2016; 6:37925. [PMID: 27901091 PMCID: PMC5128801 DOI: 10.1038/srep37925] [Citation(s) in RCA: 176] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2016] [Accepted: 11/02/2016] [Indexed: 01/28/2023] Open
Abstract
Large anisotropic exchange in 5d and 4d oxides and halides open the door to new types of magnetic ground states and excitations, inconceivable a decade ago. A prominent case is the Kitaev spin liquid, host of remarkable properties such as protection of quantum information and the emergence of Majorana fermions. Here we discuss the promise for spin-liquid behavior in the 4d5 honeycomb halide α-RuCl3. From advanced electronic-structure calculations, we find that the Kitaev interaction is ferromagnetic, as in 5d5 iridium honeycomb oxides, and indeed defines the largest superexchange energy scale. A ferromagnetic Kitaev coupling is also supported by a detailed analysis of the field-dependent magnetization. Using exact diagonalization and density-matrix renormalization group techniques for extended Kitaev-Heisenberg spin Hamiltonians, we find indications for a transition from zigzag order to a gapped spin liquid when applying magnetic field. Our results offer a unified picture on recent magnetic and spectroscopic measurements on this material and open new perspectives on the prospect of realizing quantum spin liquids in d5 halides and oxides in general.
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Affiliation(s)
- Ravi Yadav
- Institute for Theoretical Solid State Physics, IFW Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany
| | - Nikolay A Bogdanov
- Institute for Theoretical Solid State Physics, IFW Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany
| | - Vamshi M Katukuri
- Institute for Theoretical Solid State Physics, IFW Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany
| | - Satoshi Nishimoto
- Institute for Theoretical Solid State Physics, IFW Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany.,Department of Physics, Technical University Dresden, Helmholtzstrasse 10, 01069 Dresden, Germany
| | - Jeroen van den Brink
- Institute for Theoretical Solid State Physics, IFW Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany.,Department of Physics, Technical University Dresden, Helmholtzstrasse 10, 01069 Dresden, Germany.,Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
| | - Liviu Hozoi
- Institute for Theoretical Solid State Physics, IFW Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany
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72
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Giant suppression of phononic heat transport in a quantum magnet BiCu 2PO 6. Sci Rep 2016; 6:36970. [PMID: 27845377 PMCID: PMC5109484 DOI: 10.1038/srep36970] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2016] [Accepted: 10/18/2016] [Indexed: 11/13/2022] Open
Abstract
Thermal transport of quantum magnets has elucidated the nature of low energy elementary excitations and complex interplay between those excited states via strong scattering of thermal carriers. BiCu2PO6 is a unique frustrated spin-ladder compound exhibiting highly anisotropic spin excitations that contain both itinerant and localized dispersion characters along the b- and a-axes respectively. Here, we investigate thermal conductivity κ of BiCu2PO6 under high magnetic fields (H) of up to 30 tesla. A dip-feature in κ, located at ~15 K at zero-H along all crystallographic directions, moves gradually toward lower temperature (T) with increasing H, thus resulting in giant suppression by a factor of ~30 near the critical magnetic field of Hc ≅ 23.5 tesla. The giant H- and T-dependent suppression of κ can be explained by the combined result of resonant scattering of phononic heat carriers with magnetic energy levels and increased phonon scattering due to enhanced spin fluctuation at Hc, unequivocally revealing the existence of strong spin-phonon coupling. Moreover, we find an experimental indication that the remaining magnetic heat transport along the b-axis becomes almost gapless at the magnetic quantum critical point realized at Hc.
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73
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Lee TH, Florens S, Dobrosavljević V. Fate of Spinons at the Mott Point. PHYSICAL REVIEW LETTERS 2016; 117:136601. [PMID: 27715107 DOI: 10.1103/physrevlett.117.136601] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2016] [Indexed: 06/06/2023]
Abstract
Gapless spin liquids have recently been observed in several frustrated Mott insulators, with elementary spin excitations-"spinons"-reminiscent of degenerate Fermi systems. However, their precise role at the Mott point, where charge fluctuations begin to proliferate, remains controversial and ill understood. Here we present the simplest theoretical framework that treats the dynamics of emergent spin and charge excitations on the same footing, providing a new physical picture of the Mott metal-to-insulator transition at half filing. We identify a generic orthogonality mechanism leading to strong damping of spinons, arising as soon as the Mott gap closes. Our results indicate that spinons should not play a significant role within the high-temperature quantum critical regime above the Mott point-in striking agreement with all available experiments.
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Affiliation(s)
- Tsung-Han Lee
- Department of Physics and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA
| | - Serge Florens
- Institut Néel, CNRS and Université Grenoble Alpes, F-38042 Grenoble, France
| | - Vladimir Dobrosavljević
- Department of Physics and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA
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74
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Postulka L, Winter SM, Mihailov AG, Mailman A, Assoud A, Robertson CM, Wolf B, Lang M, Oakley RT. Spin Frustration in an Organic Radical Ion Salt Based on a Kagome-Coupled Chain Structure. J Am Chem Soc 2016; 138:10738-41. [PMID: 27537064 DOI: 10.1021/jacs.6b05079] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Electro-oxidation of the quinoidal bisdithiazole BT in dichloroethane in the presence of [Bu4N][GaBr4] affords the 1:1 radical ion salt [BT][GaBr4], crystals of which belong to the trigonal space group P3. The packing pattern of the radical cations provides a rare example of an organic kagome basket structure, with S = 1/2 radical ion chains located at the triangular corners of a trihexagonal lattice. Magnetic measurements over a wide temperature range from 30 mK to 300 K suggest strongly frustrated AFM interactions on the scale of J/kb ∼ 30 K, but reveal no anomalies that would be associated with magnetic order. These observations are discussed in terms of the symmetry allowed magnetic interactions within and between the frustrated layers.
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Affiliation(s)
- Lars Postulka
- Physikalisches Institut, Goethe-Universität , Frankfurt 60438, Germany
| | - Stephen M Winter
- Physikalisches Institut, Goethe-Universität , Frankfurt 60438, Germany
| | - Adam G Mihailov
- Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada
| | - Aaron Mailman
- Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada
| | - Abdeljalil Assoud
- Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada
| | - Craig M Robertson
- Department of Chemistry, University of Liverpool , Liverpool L69 7ZD, United Kingdom
| | - Bernd Wolf
- Physikalisches Institut, Goethe-Universität , Frankfurt 60438, Germany
| | - Michael Lang
- Physikalisches Institut, Goethe-Universität , Frankfurt 60438, Germany
| | - Richard T Oakley
- Department of Chemistry, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada
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75
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Raman spectroscopic signature of fractionalized excitations in the harmonic-honeycomb iridates β- and γ-Li2IrO3. Nat Commun 2016; 7:12286. [PMID: 27457278 PMCID: PMC4963532 DOI: 10.1038/ncomms12286] [Citation(s) in RCA: 74] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2016] [Accepted: 06/20/2016] [Indexed: 11/25/2022] Open
Abstract
The fractionalization of elementary excitations in quantum spin systems is a central theme in current condensed matter physics. The Kitaev honeycomb spin model provides a prominent example of exotic fractionalized quasiparticles, composed of itinerant Majorana fermions and gapped gauge fluxes. However, identification of the Majorana fermions in a three-dimensional honeycomb lattice remains elusive. Here we report spectroscopic signatures of fractional excitations in the harmonic-honeycomb iridates β- and γ-Li2IrO3. Using polarization-resolved Raman spectroscopy, we find that the dynamical Raman response of β- and γ-Li2IrO3 features a broad scattering continuum with distinct polarization and composition dependence. The temperature dependence of the Raman spectral weight is dominated by the thermal damping of fermionic excitations. These results suggest the emergence of Majorana fermions from spin fractionalization in a three-dimensional Kitaev–Heisenberg system. Fractional excitations in quantum spin systems lead to exotic particles predicted in theory but difficult to observe in experiments. Here, Glamazda et al. report the dynamical Raman response of β- and γ-Li2IrO3 is dominated by thermal damping of fermionic excitations, suggesting the emergence of Majorana fermions from spin fractionalization.
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76
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Emergence of nontrivial magnetic excitations in a spin-liquid state of kagomé volborthite. Proc Natl Acad Sci U S A 2016; 113:8653-7. [PMID: 27439874 DOI: 10.1073/pnas.1524076113] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
When quantum fluctuations destroy underlying long-range ordered states, novel quantum states emerge. Spin-liquid (SL) states of frustrated quantum antiferromagnets, in which highly correlated spins fluctuate down to very low temperatures, are prominent examples of such quantum states. SL states often exhibit exotic physical properties, but the precise nature of the elementary excitations behind such phenomena remains entirely elusive. Here, we use thermal Hall measurements that can capture the unexplored property of the elementary excitations in SL states, and report the observation of anomalous excitations that may unveil the unique features of the SL state. Our principal finding is a negative thermal Hall conductivity [Formula: see text] which the charge-neutral spin excitations in a gapless SL state of the 2D kagomé insulator volborthite Cu3V2O7(OH)2[Formula: see text]2H2O exhibit, in much the same way in which charged electrons show the conventional electric Hall effect. We find that [Formula: see text] is absent in the high-temperature paramagnetic state and develops upon entering the SL state in accordance with the growth of the short-range spin correlations, demonstrating that [Formula: see text] is a key signature of the elementary excitation formed in the SL state. These results suggest the emergence of nontrivial elementary excitations in the gapless SL state which feel the presence of fictitious magnetic flux, whose effective Lorentz force is found to be less than 1/100 of the force experienced by free electrons.
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77
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Banerjee A, Bridges CA, Yan JQ, Aczel AA, Li L, Stone MB, Granroth GE, Lumsden MD, Yiu Y, Knolle J, Bhattacharjee S, Kovrizhin DL, Moessner R, Tennant DA, Mandrus DG, Nagler SE. Proximate Kitaev quantum spin liquid behaviour in a honeycomb magnet. NATURE MATERIALS 2016; 15:733-740. [PMID: 27043779 DOI: 10.1038/nmat4604] [Citation(s) in RCA: 210] [Impact Index Per Article: 26.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Accepted: 02/22/2016] [Indexed: 06/05/2023]
Abstract
Quantum spin liquids (QSLs) are topological states of matter exhibiting remarkable properties such as the capacity to protect quantum information from decoherence. Whereas their featureless ground states have precluded their straightforward experimental identification, excited states are more revealing and particularly interesting owing to the emergence of fundamentally new excitations such as Majorana fermions. Ideal probes of these excitations are inelastic neutron scattering experiments. These we report here for a ruthenium-based material, α-RuCl3, continuing a major search (so far concentrated on iridium materials) for realizations of the celebrated Kitaev honeycomb topological QSL. Our measurements confirm the requisite strong spin-orbit coupling and low-temperature magnetic order matching predictions proximate to the QSL. We find stacking faults, inherent to the highly two-dimensional nature of the material, resolve an outstanding puzzle. Crucially, dynamical response measurements above interlayer energy scales are naturally accounted for in terms of deconfinement physics expected for QSLs. Comparing these with recent dynamical calculations involving gauge flux excitations and Majorana fermions of the pure Kitaev model, we propose the excitation spectrum of α-RuCl3 as a prime candidate for fractionalized Kitaev physics.
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Affiliation(s)
- A Banerjee
- Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA
| | - C A Bridges
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA
| | - J-Q Yan
- Material Sciences and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA
- Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA
| | - A A Aczel
- Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA
| | - L Li
- Department of Physics, University of Tennessee, Knoxville, Tennessee 37996, USA
| | - M B Stone
- Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA
| | - G E Granroth
- Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA
- Neutron Data Analysis &Visualization Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA
| | - M D Lumsden
- Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA
| | - Y Yiu
- Department of Physics, University of Tennessee, Knoxville, Tennessee 37996, USA
| | - J Knolle
- Department of Physics, Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, UK
| | - S Bhattacharjee
- Max Planck Institute for the Physics of Complex Systems, D-01187 Dresden, Germany
- International Center for Theoretical Sciences, TIFR, Bangalore 560012, India
| | - D L Kovrizhin
- Department of Physics, Cavendish Laboratory, J.J. Thomson Avenue, Cambridge CB3 0HE, UK
| | - R Moessner
- Max Planck Institute for the Physics of Complex Systems, D-01187 Dresden, Germany
| | - D A Tennant
- Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA
| | - D G Mandrus
- Material Sciences and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA
- Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, USA
| | - S E Nagler
- Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, USA
- Bredesen Center, University of Tennessee, Knoxville, Tennessee 37966, USA
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78
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Possible observation of highly itinerant quantum magnetic monopoles in the frustrated pyrochlore Yb2Ti2O7. Nat Commun 2016; 7:10807. [PMID: 26912080 PMCID: PMC4773418 DOI: 10.1038/ncomms10807] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2015] [Accepted: 01/22/2016] [Indexed: 11/20/2022] Open
Abstract
The low-energy elementary excitations in frustrated quantum magnets have fascinated researchers for decades. In frustrated Ising magnets on a pyrochlore lattice possessing macroscopically degenerate spin-ice ground states, the excitations have been discussed in terms of classical magnetic monopoles, which do not contain quantum fluctuations. Here we report unusual behaviours of magneto-thermal conductivity in the disordered spin-liquid regime of pyrochlore Yb2Ti2O7, which hosts frustrated spin-ice correlations with large quantum fluctuations owing to pseudospin-1/2 of Yb ions. The analysis of the temperature and magnetic field dependencies shows the presence of gapped elementary excitations. We find that the gap energy is largely suppressed from that expected in classical monopoles. Moreover, these excitations propagate a long distance without being scattered, in contrast to the diffusive nature of classical monopoles. These results suggests the emergence of highly itinerant quantum magnetic monopole, which is a heavy quasiparticle that propagates coherently in three-dimensional spin liquids. Spin excitations above the ground state of spin ices, geometrically frustrated pyrochlore magnets, are equivalent to pairs of oppositely charged deconfined magnetic monopoles which may propagate through the system. Here, the authors evidence highly itinerant quantum magnetic monopole excitations in Yb2Ti2O7.
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79
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Wu JC, Song JD, Zhao ZY, Shi J, Xu HS, Zhao JY, Liu XG, Zhao X, Sun XF. Thermal conductivity of the diamond-chain compound Cu₃(CO₃)₂(OH)₂. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2016; 28:056002. [PMID: 26761589 DOI: 10.1088/0953-8984/28/5/056002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Thermal conductivity (κ) of a distorted spin diamond-chain system, Cu3(CO3)2(OH)2, is studied at low temperatures down to 0.3 K and in magnetic fields up to 14 T. In zero field, the κ(T) curve with heat current along the chain direction has very small magnitudes and shows a pronounced three-peak structure. The magnetic fields along and perpendicular to the chains change the κ strongly in a way having good correspondence to the changes of magnetic specific heat in fields. The data analysis based on the Debye model for phononic thermal conductivity indicates that the heat transport is due to phonons and the three-peak structure is caused by two resonant scattering processes by the magnetic excitations. In particular, the spin excitations of the chain subsystem are strongly scattering phonons rather than transporting heat.
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Affiliation(s)
- J C Wu
- Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China
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80
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Quantum electric-dipole liquid on a triangular lattice. Nat Commun 2016; 7:10569. [PMID: 26843363 PMCID: PMC4743005 DOI: 10.1038/ncomms10569] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2015] [Accepted: 12/26/2015] [Indexed: 11/30/2022] Open
Abstract
Geometric frustration and quantum fluctuations may prohibit the formation of long-range ordering even at the lowest temperature, and therefore liquid-like ground states could be expected. A good example is the quantum spin liquid in frustrated magnets. Geometric frustration and quantum fluctuations can happen beyond magnetic systems. Here we propose that quantum electric-dipole liquids, analogues of quantum spin liquids, could emerge in frustrated dielectrics where antiferroelectrically coupled electric dipoles reside on a triangular lattice. The quantum paraelectric hexaferrite BaFe12O19 with geometric frustration represents a promising candidate for the proposed electric-dipole liquid. We present a series of experimental lines of evidence, including dielectric permittivity, heat capacity and thermal conductivity measured down to 66 mK, to reveal the existence of an unusual liquid-like quantum phase in BaFe12O19, characterized by itinerant low-energy excitations with a small gap. The possible quantum liquids of electric dipoles in frustrated dielectrics open up a fresh playground for fundamental physics. In magnetic materials, geometry-defined competing interactions between spins combined with quantum fluctuations can present the possibility of quantum liquid states which do not order even as 0K is approached. Here, the authors present an analogue built from electric dipoles on a triangular lattice.
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81
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Sibille R, Lhotel E, Pomjakushin V, Baines C, Fennell T, Kenzelmann M. Candidate Quantum Spin Liquid in the Ce3+ Pyrochlore Stannate Ce2Sn2O7. PHYSICAL REVIEW LETTERS 2015; 115:097202. [PMID: 26371677 DOI: 10.1103/physrevlett.115.097202] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2015] [Indexed: 06/05/2023]
Abstract
We report the low-temperature magnetic properties of Ce2Sn2O7, a rare-earth pyrochlore. Our susceptibility and magnetization measurements show that due to the thermal isolation of a Kramers doublet ground state, Ce2Sn2O7 has Ising-like magnetic moments of ∼1.18 μ_{B}. The magnetic moments are confined to the local trigonal axes, as in a spin ice, but the exchange interactions are antiferromagnetic. Below 1 K, the system enters a regime with antiferromagnetic correlations. In contrast to predictions for classical ⟨111⟩-Ising spins on the pyrochlore lattice, there is no sign of long-range ordering down to 0.02 K. Our results suggest that Ce2Sn2O7 features an antiferromagnetic liquid ground state with strong quantum fluctuations.
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Affiliation(s)
- Romain Sibille
- Laboratory for Scientific Developments and Novel Materials, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
| | - Elsa Lhotel
- Institut Néel, CNRS, and Université Joseph Fourier, BP 166, 38042 Grenoble Cedex 9, France
| | - Vladimir Pomjakushin
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
| | - Chris Baines
- Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
| | - Tom Fennell
- Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
| | - Michel Kenzelmann
- Laboratory for Scientific Developments and Novel Materials, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland
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82
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Furukawa T, Miyagawa K, Itou T, Ito M, Taniguchi H, Saito M, Iguchi S, Sasaki T, Kanoda K. Quantum Spin Liquid Emerging from Antiferromagnetic Order by Introducing Disorder. PHYSICAL REVIEW LETTERS 2015; 115:077001. [PMID: 26317741 DOI: 10.1103/physrevlett.115.077001] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2015] [Indexed: 06/04/2023]
Abstract
Quantum spin liquids, which are spin versions of quantum matter, have been sought after in systems with geometrical frustration. We show that disorder drives a classical magnet into a quantum spin liquid through conducting NMR experiments on an organic Mott insulator, κ-(ET)_{2}Cu[N(CN)_{2}]Cl. Antiferromagnetic ordering in the pristine crystal, when irradiated by x rays, disappears. Spin freezing, spin gap, and critical slowing down are not observed, but gapless spin excitations emerge, suggesting a novel role of disorder that brings forth a quantum spin liquid from a classical ordered state.
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Affiliation(s)
- T Furukawa
- Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
| | - K Miyagawa
- Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
| | - T Itou
- Department of Applied Physics, Tokyo University of Science, Tokyo 125-8585, Japan
| | - M Ito
- Department of Physics, Saitama University, Saitama 338-8570, Japan
| | - H Taniguchi
- Department of Physics, Saitama University, Saitama 338-8570, Japan
| | - M Saito
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - S Iguchi
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - T Sasaki
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - K Kanoda
- Department of Applied Physics, University of Tokyo, Tokyo 113-8656, Japan
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83
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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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84
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Nasu J, Udagawa M, Motome Y. Vaporization of Kitaev spin liquids. PHYSICAL REVIEW LETTERS 2014; 113:197205. [PMID: 25415923 DOI: 10.1103/physrevlett.113.197205] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2014] [Indexed: 06/04/2023]
Abstract
The quantum spin liquid is an exotic quantum state of matter in magnets. This state is a spin analog of liquid helium that does not solidify down to the lowest temperature due to strong quantum fluctuations. In conventional fluids, the liquid and gas possess the same symmetry and adiabatically connect to each other by bypassing the critical end point. We find that the situation is qualitatively different in quantum spin liquids realized in a three-dimensional Kitaev model; both gapless and gapped quantum spin liquid phases at low temperatures are always distinguished from the high-temperature paramagnet (spin gas) by a phase transition. The results challenge the common belief that the absence of thermodynamic singularity down to the lowest temperature is a symptom of a quantum spin liquid.
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Affiliation(s)
- Joji Nasu
- Department of Physics, Tokyo Institute of Technology, Ookayama, 2-12-1, Meguro, Tokyo 152-8551, Japan
| | - Masafumi Udagawa
- Department of Applied Physics, University of Tokyo, Hongo, 7-3-1, Bunkyo, Tokyo 113-8656, Japan
| | - Yukitoshi Motome
- Department of Applied Physics, University of Tokyo, Hongo, 7-3-1, Bunkyo, Tokyo 113-8656, Japan
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85
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Candidate quantum spin liquid due to dimensional reduction of a two-dimensional honeycomb lattice. Sci Rep 2014; 4:6451. [PMID: 25245216 PMCID: PMC5377320 DOI: 10.1038/srep06451] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Accepted: 09/02/2014] [Indexed: 11/11/2022] Open
Abstract
As with quantum spin liquids based on two-dimensional triangular and kagome lattices, the two-dimensional honeycomb lattice with either a strong spin-orbital coupling or a frustrating second-nearest-neighbor coupling is expected to be a source of candidate quantum spin liquids. An ammonium salt [(C3H7)3NH]2[Cu2(C2O4)3](H2O)2.2 containing hexagonal layers of Cu2+ was obtained from solution. No structural transition or long-range magnetic ordering was observed from 290 K to 2 K from single crystal X-ray diffraction, specific heat and susceptibility measurements. The anionic layers are separated by sheets of ammonium and H2O with distance of 3.5 Å and no significant interaction between anionic layers. The two-dimensional honeycomb lattice is constructed from Jahn-Teller distorted Cu2+ and oxalate anions, showing a strong antiferromagnetic interaction between S = 1/2 metal atoms with θ = −120 (1) K. Orbital analysis of the Cu2+ interactions through the oxalate-bridges suggests a stripe mode pattern of coupling with weak ferromagnetic interaction along the b axis, and strong antiferromagnetic interaction along the a axis. Analysis of the magnetic susceptibility shows that it is dominated by a quasi-one-dimensional contribution with spin chains that are at least as well isolated as those of well-known quasi-one-dimensional spin liquids.
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86
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Clark L, Nilsen GJ, Kermarrec E, Ehlers G, Knight KS, Harrison A, Attfield JP, Gaulin BD. From spin glass to quantum spin liquid ground states in molybdate pyrochlores. PHYSICAL REVIEW LETTERS 2014; 113:117201. [PMID: 25260001 DOI: 10.1103/physrevlett.113.117201] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2014] [Indexed: 06/03/2023]
Abstract
We present new magnetic heat capacity and neutron scattering results for two magnetically frustrated molybdate pyrochlores: S=1 oxide Lu_{2}Mo_{2}O_{7} and S=1/2 oxynitride Lu_{2}Mo_{2}O_{5}N_{2}. Lu_{2}Mo_{2}O_{7} undergoes a transition to an unconventional spin glass ground state at T_{f}∼16 K. However, the preparation of the corresponding oxynitride tunes the nature of the ground state from spin glass to quantum spin liquid. The comparison of the static and dynamic spin correlations within the oxide and oxynitride phases presented here reveals the crucial role played by quantum fluctuations in the selection of a ground state. Furthermore, we estimate an upper limit for a gap in the spin excitation spectrum of the quantum spin liquid state of the oxynitride of Δ∼0.05 meV or Δ/|θ|∼0.004, in units of its antiferromagnetic Weiss constant θ∼-121 K.
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Affiliation(s)
- L Clark
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
| | - G J Nilsen
- Institute Laue-Langevin, 6 Rue Jules Horowitz, 38042 Grenoble, France
| | - E Kermarrec
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada
| | - G Ehlers
- Neutron Scattering Science Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA
| | - K S Knight
- ISIS Facility, Rutherford Appleton Laboratory, Didcot, Oxfordshire OX11 0QX, United Kingdom
| | - A Harrison
- CSEC and School of Chemistry, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ, United Kingdom and Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Oxfordshire OX11 0QX, United Kingdom
| | - J P Attfield
- CSEC and School of Chemistry, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ, United Kingdom
| | - B D Gaulin
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1, Canada and Brockhouse Institute for Materials Research, Hamilton, Ontario L8S 4M1, Canada and Canadian Institute for Advanced Research, 180 Dundas Street West, Toronto, Ontario M5G 1Z8, Canada
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87
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88
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Spin-orbital entangled molecular jeff states in lacunar spinel compounds. Nat Commun 2014; 5:3988. [PMID: 24889209 DOI: 10.1038/ncomms4988] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2013] [Accepted: 04/29/2014] [Indexed: 11/08/2022] Open
Abstract
The entanglement of the spin and orbital degrees of freedom through the spin-orbit coupling has been actively studied in condensed matter physics. In several iridium oxide systems, the spin-orbital entangled state, identified by the effective angular momentum jeff, can host novel quantum phases. Here we show that a series of lacunar spinel compounds, GaM4X8 (M=Nb, Mo, Ta and W and X=S, Se and Te), gives rise to a molecular jeff state as a new spin-orbital composite on which the low-energy effective Hamiltonian is based. A wide range of electron correlations is accessible by tuning the bandwidth under external and/or chemical pressure, enabling us to investigate the cooperation between spin-orbit coupling and electron correlations. As illustrative examples, a two-dimensional topological insulating phase and an anisotropic spin Hamiltonian are investigated in the weak and strong coupling regimes, respectively. Our finding can provide an ideal platform for exploring jeff physics and the resulting emergent phenomena.
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89
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Isono T, Kamo H, Ueda A, Takahashi K, Kimata M, Tajima H, Tsuchiya S, Terashima T, Uji S, Mori H. Gapless quantum spin liquid in an organic spin-1/2 triangular-lattice κ-H3(Cat-EDT-TTF)2. PHYSICAL REVIEW LETTERS 2014; 112:177201. [PMID: 24836269 DOI: 10.1103/physrevlett.112.177201] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2013] [Indexed: 06/03/2023]
Abstract
We report the results of SQUID and torque magnetometry of an organic spin-1/2 triangular-lattice κ-H(3)(Cat-EDT-TTF)(2). Despite antiferromagnetic exchange coupling at 80-100 K, we observed no sign of antiferromagnetic order down to 50 mK owing to spin frustration on the triangular lattice. In addition, we found nearly temperature-independent susceptibility below 3 K associated with Pauli paramagnetism. These observations suggest the development of gapless quantum spin liquid as the ground state. On the basis of a comparative discussion, we point out that the gapless quantum spin liquid states in organic systems share a possible mechanism, namely the formation of a band with a Fermi surface possibly attributed to spinons.
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Affiliation(s)
- Takayuki Isono
- The Institute for Solid State Physics (ISSP), The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - Hiromichi Kamo
- The Institute for Solid State Physics (ISSP), The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - Akira Ueda
- The Institute for Solid State Physics (ISSP), The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | | | - Motoi Kimata
- The Institute for Solid State Physics (ISSP), The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - Hiroyuki Tajima
- The Institute for Solid State Physics (ISSP), The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
| | - Satoshi Tsuchiya
- National Institute for Materials Science, Tsukuba, Ibaraki 305-0003, Japan
| | - Taichi Terashima
- National Institute for Materials Science, Tsukuba, Ibaraki 305-0003, Japan
| | - Shinya Uji
- National Institute for Materials Science, Tsukuba, Ibaraki 305-0003, Japan
| | - Hatsumi Mori
- The Institute for Solid State Physics (ISSP), The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
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90
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Kato R. Development of π-Electron Systems Based on [M(dmit)2] (M = Ni and Pd; dmit: 1,3-dithiole-2-thione-4,5-dithiolate) Anion Radicals. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 2014. [DOI: 10.1246/bcsj.20130290] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Affiliation(s)
- Reizo Kato
- Condensed Molecular Materials Laboratory, RIKEN
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91
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Chen Y, Cao F, Wei RM, Zhang Y, Zhang YQ, Song Y. Spin-crossover phenomena of the mononuclear Mn(III) complex tuned by metal dithiolene counteranions. Dalton Trans 2014; 43:3783-91. [PMID: 24441029 DOI: 10.1039/c3dt53173b] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Three ion-pair complexes based on spin-crossover [Mn(5-Br-sal-N-1,5,8,12)]ClO4 with TBA2[Ni(mnt)2], TBA2[Pt(mnt)2] (mnt = maleonitriledithiolate) and TBA[Ni(dmit)2] respectively (dmit = 2-thioxo-1,3-dithiole-4,5-dithiolato) have been synthesized and structurally characterized. Complexes [Mn(5-Br-sal-N-1,5,8,12)]2[Ni(mnt)2] and [Mn(5-Br-sal-N-1,5,8,12)]2[Pt(mnt)2] are isomorphic and show the axial compression of the octahedral coordination environment of Mn(III) ions. With the temperature increasing the equatorial metal-ligand bond lengths show significant elongation, but the axial bond lengths remain unchanged. Complex [Mn(5-Br-sal-N-1,5,8,12)][Ni(dmit)2]·CH3CN contains π-π, p-π and H-bonds weak interactions. Magnetic investigation shows the spin-crossover phenomena for and , and T1/2 has been increased by 230 K comparing with the reactant complex. However, no spin-crossover was observed in complex , and theoretical calculations show that there are weak antiferromagnetic couplings mediated through π-π interactions.
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Affiliation(s)
- Ying Chen
- State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructures and School of Chemistry and Chemical Engineering, Nanjing University, Hankou Road 22, Nanjing, 210093, P. R. China.
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92
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Zvyagin SA, Kamenskyi D, Ozerov M, Wosnitza J, Ikeda M, Fujita T, Hagiwara M, Smirnov AI, Soldatov TA, Shapiro AY, Krzystek J, Hu R, Ryu H, Petrovic C, Zhitomirsky ME. Direct determination of exchange parameters in Cs2CuBr4 and Cs2CuCl4: high-field electron-spin-resonance studies. PHYSICAL REVIEW LETTERS 2014; 112:077206. [PMID: 24579634 DOI: 10.1103/physrevlett.112.077206] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2013] [Indexed: 06/03/2023]
Abstract
Spin-1/2 Heisenberg antiferromagnets Cs2CuCl4 and Cs2CuBr4 with distorted triangular-lattice structures are studied by means of electron spin resonance spectroscopy in magnetic fields up to the saturation field and above. In the magnetically saturated phase, quantum fluctuations are fully suppressed, and the spin dynamics is defined by ordinary magnons. This allows us to accurately describe the magnetic excitation spectra in both materials and, using the harmonic spin-wave theory, to determine their exchange parameters. The viability of the proposed method was proven by applying it to Cs2CuCl4, yielding J/kB=4.7(2) K, J'/kB=1.42(7) K, [J'/J≃0.30] and revealing good agreement with inelastic neutron-scattering results. For the isostructural Cs2CuBr4, we obtain J/kB=14.9(7) K, J'/kB=6.1(3) K, [J'/J≃0.41], providing exact and conclusive information on the exchange couplings in this frustrated spin system.
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Affiliation(s)
- S A Zvyagin
- Dresden High Magnetic Field Laboratory (HLD), Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany
| | - D Kamenskyi
- Dresden High Magnetic Field Laboratory (HLD), Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany
| | - M Ozerov
- Dresden High Magnetic Field Laboratory (HLD), Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany
| | - J Wosnitza
- Dresden High Magnetic Field Laboratory (HLD), Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany and Institüt fur Festkörperphysik, TU Dresden, 01068 Dresden, Germany
| | - M Ikeda
- KYOKUGEN, Osaka University, Toyonaka, Osaka 560-8531, Japan
| | - T Fujita
- KYOKUGEN, Osaka University, Toyonaka, Osaka 560-8531, Japan
| | - M Hagiwara
- KYOKUGEN, Osaka University, Toyonaka, Osaka 560-8531, Japan
| | - A I Smirnov
- P.L. Kapitza Institute for Physical Problems, RAS, 119334 Moscow, Russia
| | - T A Soldatov
- Moscow Institute for Physics and Technology, 141700 Dolgoprudnyi, Russia
| | - A Ya Shapiro
- A.V. Shubnikov Institute of Crystallography, RAS, 119333, Moscow, Russia
| | - J Krzystek
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA
| | - R Hu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA
| | - H Ryu
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA and Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794-3800, USA
| | - C Petrovic
- Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA and Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794-3800, USA
| | - M E Zhitomirsky
- Service de Physique Statistique, Magnétisme et Supraconductivité, UMR-E9001 CEA-INAC/UJF, 38054 Grenoble Cedex 9, France
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93
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Nakazawa Y, Yamashita S. Thermodynamics of a Liquid-like Spin State in Molecule-based Magnets with Geometric Frustrations. CHEM LETT 2013. [DOI: 10.1246/cl.130656] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Yasuhiro Nakazawa
- Department of Chemistry, Graduate School of Science, Osaka University
| | - Satoshi Yamashita
- Department of Chemistry, Graduate School of Science, Osaka University
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94
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Mishmash RV, Garrison JR, Bieri S, Xu C. Theory of a competitive spin liquid state for weak Mott insulators on the triangular lattice. PHYSICAL REVIEW LETTERS 2013; 111:157203. [PMID: 24160624 DOI: 10.1103/physrevlett.111.157203] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2013] [Indexed: 06/02/2023]
Abstract
We propose a novel quantum spin liquid state that can explain many of the intriguing experimental properties of the low-temperature phase of the organic spin liquid candidate materials κ-(BEDT-TTF)2Cu2(CN)3 and EtMe3Sb[Pd(dmit)2]2. This state of paired fermionic spinons preserves all symmetries of the system, and it has a gapless excitation spectrum with quadratic bands that touch at momentum k[over →]=0. This quadratic band touching is protected by symmetries. Using variational Monte Carlo techniques, we show that this state has highly competitive energy in the triangular lattice Heisenberg model supplemented with a realistically large ring-exchange term.
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Affiliation(s)
- Ryan V Mishmash
- Department of Physics, University of California, Santa Barbara, California 93106, USA
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95
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Pilon DV, Lui CH, Han TH, Shrekenhamer D, Frenzel AJ, Padilla WJ, Lee YS, Gedik N. Spin-induced optical conductivity in the spin-liquid candidate herbertsmithite. PHYSICAL REVIEW LETTERS 2013; 111:127401. [PMID: 24093299 DOI: 10.1103/physrevlett.111.127401] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2013] [Indexed: 06/02/2023]
Abstract
We report a direct measurement of the low-frequency optical conductivity of large-area single-crystal herbertsmithite, a promising spin-liquid candidate material, by means of terahertz time-domain spectroscopy. In the spectral range below 1.4 THz, we observe a contribution to the real part of the in-plane conductivity σ(ab)(ω) from the spin degree of freedom. This spin-induced conductivity exhibits a power-law dependence on frequency σ(ab)(ω) ~ ω(β) with β ≈ 1.4. Our observation is consistent with the theoretically predicted low-frequency conductivity arising from an emergent gauge field of a gapless U(1) Dirac spin liquid.
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Affiliation(s)
- D V Pilon
- Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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96
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Abstract
We compute the entanglement entropy of a wide class of models that may be characterized as describing matter coupled to gauge fields. Our principle result is an entanglement sum rule that states that the entropy of the full system is the sum of the entropies of the two components. In the context of the models we consider, this result applies to the full entropy, but more generally it is a statement about the additivity of universal terms in the entropy. Our proof simultaneously extends and simplifies previous arguments, with extensions including new models at zero temperature as well as the ability to treat finite temperature crossovers. We emphasize that while the additivity is an exact statement, each term in the sum may still be difficult to compute. Our results apply to a wide variety of phases including Fermi liquids, spin liquids, and some non-Fermi liquid metals. For example, we prove that our model of an interacting Fermi liquid has exactly the log violation of the area law for entanglement entropy predicted by the Widom formula in agreement with earlier arguments.
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Affiliation(s)
- Brian Swingle
- Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA
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97
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Fujita W, Kikuchi K. New Layered Copper Hydroxide with S = 1/2 Two-Dimensional Triangular Lattice Magnetic Network, [Cu7(OH)12(CH3CH2CO2)2]·(CH3CH2CO2H)2·(H2O)6. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 2013. [DOI: 10.1246/bcsj.20130062] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Wataru Fujita
- Department of Chemistry, Tokyo Metropolitan University
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98
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Watanabe D, Yamashita M, Tonegawa S, Oshima Y, Yamamoto HM, Kato R, Sheikin I, Behnia K, Terashima T, Uji S, Shibauchi T, Matsuda Y. Novel Pauli-paramagnetic quantum phase in a Mott insulator. Nat Commun 2013; 3:1090. [PMID: 23011144 DOI: 10.1038/ncomms2082] [Citation(s) in RCA: 60] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2012] [Accepted: 08/22/2012] [Indexed: 11/09/2022] Open
Abstract
In Mott insulators, the strong electron-electron Coulomb repulsion localizes electrons. In dimensions greater than one, their spins are usually ordered antiferromagnetically at low temperatures. Geometrical frustrations can destroy this long-range order, leading to exotic quantum spin liquid states. However, their magnetic ground states have been a long-standing mystery. Here we show that a quantum spin liquid state in the organic Mott insulator EtMe(3)Sb[Pd(dmit)(2)](2) (where Et is C(2)H(5)-, Me is CH(3)-, and dmit is 1,3-dithiole-2-thione-4,5-dithiolate) with two-dimensional triangular lattice has Pauli-paramagnetic-like low-energy excitations, which are a hallmark of itinerant fermions. Our torque magnetometry down to low temperatures (30 mK) up to high fields (32 T) reveals distinct residual paramagnetic susceptibility comparable to that in a half-filled two-dimensional metal, demonstrating the magnetically gapless nature of the ground state. Moreover, our results are robust against deuteration, pointing toward the emergence of an extended 'quantum critical phase', in which low-energy spin excitations behave as in paramagnetic metals with Fermi surface, despite the frozen charge degree of freedom.
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Affiliation(s)
- D Watanabe
- Department of Physics, Kyoto University, Kyoto 606-8502, Japan
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Sorai M, Nakazawa Y, Nakano M, Miyazaki Y. Update 1 of: Calorimetric Investigation of Phase Transitions Occurring in Molecule-Based Magnets. Chem Rev 2013; 113:PR41-122. [DOI: 10.1021/cr300156s] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Michio Sorai
- Research Center for Structural Thermodynamics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Yasuhiro Nakazawa
- Research Center for Structural Thermodynamics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
- Department of Chemistry, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
| | - Motohiro Nakano
- Department of Applied Chemistry,
Graduate School of Engineering, Osaka University, Suita, Osaka 565-0871,
Japan
| | - Yuji Miyazaki
- Research Center for Structural Thermodynamics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
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Lieffrig J, Pennec RL, Jeannin O, Auban-Senzier P, Fourmigué M. Toward chiral conductors: combining halogen bonding ability and chirality within a single tetrathiafulvalene molecule. CrystEngComm 2013. [DOI: 10.1039/c3ce40393a] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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