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Wang J, Spitaler M, Su YS, Zoch KM, Krellner C, Puphal P, Brown SE, Pustogow A. Controlled Frustration Release on the Kagome Lattice by Uniaxial-Strain Tuning. Phys Rev Lett 2023; 131:256501. [PMID: 38181349 DOI: 10.1103/physrevlett.131.256501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2023] [Revised: 09/26/2023] [Accepted: 11/16/2023] [Indexed: 01/07/2024]
Abstract
It is predicted that strongly interacting spins on a frustrated lattice may lead to a quantum disordered ground state or even form a quantum spin liquid with exotic low-energy excitations. However, a controlled tuning of the frustration strength, separating its effects from those of disorder and other factors, is pending. Here, we perform comprehensive ^{1}H NMR measurements on Y_{3}Cu_{9}(OH)_{19}Cl_{8} single crystals revealing an unusual Q[over →]=(1/3×1/3) antiferromagnetic state below T_{N}=2.2 K. By applying in situ uniaxial stress, we break the symmetry of this disorder-free, frustrated kagome system in a controlled manner yielding a linear increase of T_{N} with strain, in line with theoretical predictions for a distorted kagome lattice. In-plane strain of ≈1% triggers a sizable enhancement ΔT_{N}/T_{N}≈10% due to a release of frustration, demonstrating its pivotal role for magnetic order.
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Affiliation(s)
- Jierong Wang
- Department of Physics and Astronomy, UCLA, Los Angeles, California 90095, USA
| | - M Spitaler
- Institute of Solid State Physics, TU Wien, 1040 Vienna, Austria
| | - Y-S Su
- Department of Physics and Astronomy, UCLA, Los Angeles, California 90095, USA
| | - K M Zoch
- Institute of Physics, Goethe-University Frankfurt, 60438 Frankfurt (Main), Germany
| | - C Krellner
- Institute of Physics, Goethe-University Frankfurt, 60438 Frankfurt (Main), Germany
| | - P Puphal
- Institute of Physics, Goethe-University Frankfurt, 60438 Frankfurt (Main), Germany
- Max-Planck-Institute for Solid State Research, 70569 Stuttgart, Germany
| | - S E Brown
- Department of Physics and Astronomy, UCLA, Los Angeles, California 90095, USA
| | - A Pustogow
- Department of Physics and Astronomy, UCLA, Los Angeles, California 90095, USA
- Institute of Solid State Physics, TU Wien, 1040 Vienna, Austria
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Pustogow A, Kawasugi Y, Sakurakoji H, Tajima N. Chasing the spin gap through the phase diagram of a frustrated Mott insulator. Nat Commun 2023; 14:1960. [PMID: 37029139 PMCID: PMC10082190 DOI: 10.1038/s41467-023-37491-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2022] [Accepted: 03/16/2023] [Indexed: 04/09/2023] Open
Abstract
The quest for entangled spin excitations has stimulated intense research on frustrated magnetic systems. For almost two decades, the triangular-lattice Mott insulator κ-(BEDT-TTF)2Cu2(CN)3 has been one of the hottest candidates for a gapless quantum spin liquid with itinerant spinons. Very recently, however, this scenario was overturned as electron-spin-resonance (ESR) studies unveiled a spin gap, calling for reevaluation of the magnetic ground state. Here we achieve a precise mapping of this spin-gapped phase through the Mott transition by ultrahigh-resolution strain tuning. Our transport experiments reveal a reentrance of charge localization below T⋆ = 6 K associated with a gap size of 30-50 K. The negative slope of the insulator-metal boundary, dT⋆/dp < 0, evidences the low-entropy nature of the spin-singlet ground state. By tuning the enigmatic '6K anomaly' through the phase diagram of κ-(BEDT-TTF)2Cu2(CN)3, we identify it as the transition to a valence-bond-solid phase, in agreement with previous thermal expansion and magnetic resonance studies. This spin-gapped insulating state persists at T → 0 until unconventional superconductivity and metallic transport proliferate.
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Affiliation(s)
- A Pustogow
- Institute of Solid State Physics, TU Wien, 1040, Vienna, Austria.
| | - Y Kawasugi
- Department of Physics, Toho University, Funabashi, 274-8510, Chiba, Japan
- Condensed Molecular Materials Laboratory, RIKEN, Wako, Saitama, 351-0198, Japan
| | - H Sakurakoji
- Department of Physics, Toho University, Funabashi, 274-8510, Chiba, Japan
| | - N Tajima
- Department of Physics, Toho University, Funabashi, 274-8510, Chiba, Japan
- Condensed Molecular Materials Laboratory, RIKEN, Wako, Saitama, 351-0198, Japan
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Pustogow A, Luo Y, Chronister A, Su YS, Sokolov DA, Jerzembeck F, Mackenzie AP, Hicks CW, Kikugawa N, Raghu S, Bauer ED, Brown SE. Constraints on the superconducting order parameter in Sr 2RuO 4 from oxygen-17 nuclear magnetic resonance. Nature 2019; 574:72-75. [PMID: 31548658 DOI: 10.1038/s41586-019-1596-2] [Citation(s) in RCA: 54] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2019] [Accepted: 07/15/2019] [Indexed: 11/09/2022]
Abstract
Phases of matter are usually identified through spontaneous symmetry breaking, especially regarding unconventional superconductivity and the interactions from which it originates. In that context, the superconducting state of the quasi-two-dimensional and strongly correlated perovskite Sr2RuO4 is considered to be the only solid-state analogue to the superfluid 3He-A phase1,2, with an odd-parity order parameter that is unidirectional in spin space for all electron momenta and breaks time-reversal symmetry. This characterization was recently called into question by a search for an expected 'split' transition in a Sr2RuO4 crystal under in-plane uniaxial pressure, which failed to find any such evidence; instead, a dramatic rise and a peak in a single-transition temperature were observed3,4. Here we use nuclear magnetic resonance (NMR) spectroscopy of oxygen-17, which is directly sensitive to the order parameter via hyperfine coupling to the electronic spin degrees of freedom, to probe the nature of superconductivity in Sr2RuO4 and its evolution under strain. A reduction of the Knight shift is observed for all strain values and at temperatures below the critical temperature, consistent with a drop in spin polarization in the superconducting state. In unstrained samples, our results contradict a body of previous NMR work reporting no change in the Knight shift5 and the most prevalent theoretical interpretation of the order parameter as a chiral p-wave state. Sr2RuO4 is an extremely clean layered perovskite and its superconductivity emerges from a strongly correlated Fermi liquid, and our work imposes tight constraints on the order parameter symmetry of this archetypal system.
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Affiliation(s)
- A Pustogow
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, CA, USA.
| | - Yongkang Luo
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, CA, USA. .,Wuhan National High Magnetic Field Center and School of Physics, Huazhong University of Science and Technology, Wuhan, China.
| | - A Chronister
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, CA, USA
| | - Y-S Su
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, CA, USA
| | - D A Sokolov
- Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
| | - F Jerzembeck
- Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
| | - A P Mackenzie
- Max Planck Institute for Chemical Physics of Solids, Dresden, Germany.,School of Physics and Astronomy, University of St Andrews, St Andrews, UK
| | - C W Hicks
- Max Planck Institute for Chemical Physics of Solids, Dresden, Germany
| | - N Kikugawa
- National Institute for Materials Science, Tsukuba, Japan
| | - S Raghu
- Geballe Laboratory for Advanced Materials, Stanford University, Stanford, CA, USA
| | - E D Bauer
- Los Alamos National Laboratory, Los Alamos, New Mexico, USA
| | - S E Brown
- Department of Physics and Astronomy, University of California Los Angeles, Los Angeles, CA, USA.
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Pustogow A, McLeod AS, Saito Y, Basov DN, Dressel M. Internal strain tunes electronic correlations on the nanoscale. Sci Adv 2018; 4:eaau9123. [PMID: 30555919 PMCID: PMC6294596 DOI: 10.1126/sciadv.aau9123] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2018] [Accepted: 11/15/2018] [Indexed: 06/01/2023]
Abstract
In conventional metals, charge carriers basically move freely. In correlated electron materials, however, the electrons may become localized because of strong Coulomb interactions, resulting in an insulating state. Despite considerable progress in the last decades, elucidating the driving mechanisms that suppress metallic charge transport, the spatial evolution of this phase transition remains poorly understood on a microscopic scale. Here, we use cryogenic scanning near-field optical microscopy to study the metal-to-insulator transition in an electronically driven charge-ordered system with a 20-nm spatial resolution. In contrast to common mean-field considerations, we observe pronounced phase segregation with a sharp boundary between metallic and insulating regions evidencing its first-order nature. Considerable strain in the crystal spatially modulates the effective electronic correlations within a few micrometers, leading to an extended "zebra" pattern of metallic and insulating stripes. We can directly monitor the spatial strain distribution via a gradual enhancement of the optical conductivity as the energy gap is depressed. Our observations shed new light on previous analyses of correlation-driven metal-insulator transitions.
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Affiliation(s)
- A. Pustogow
- 1. Physikalisches Institut, Universität Stuttgart, 70569 Stuttgart, Germany
| | - A. S. McLeod
- University of California San Diego, La Jolla, CA 92093, U.S.A
- Department of Physics, Columbia University, New York, NY 92093, U.S.A
| | - Y. Saito
- 1. Physikalisches Institut, Universität Stuttgart, 70569 Stuttgart, Germany
- Department of Physics, Hokkaido University, Sapporo 060-0810, Japan
| | - D. N. Basov
- University of California San Diego, La Jolla, CA 92093, U.S.A
- Department of Physics, Columbia University, New York, NY 92093, U.S.A
| | - M. Dressel
- 1. Physikalisches Institut, Universität Stuttgart, 70569 Stuttgart, Germany
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Pustogow A, Bories M, Löhle A, Rösslhuber R, Zhukova E, Gorshunov B, Tomić S, Schlueter JA, Hübner R, Hiramatsu T, Yoshida Y, Saito G, Kato R, Lee TH, Dobrosavljević V, Fratini S, Dressel M. Quantum spin liquids unveil the genuine Mott state. Nat Mater 2018; 17:773-777. [PMID: 30082905 DOI: 10.1038/s41563-018-0140-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2017] [Accepted: 06/26/2018] [Indexed: 05/13/2023]
Abstract
The localization of charge carriers by electronic repulsion was suggested by Mott in the 1930s to explain the insulating state observed in supposedly metallic NiO. The Mott metal-insulator transition has been subject of intense investigations ever since1-3-not least for its relation to high-temperature superconductivity4. A detailed comparison to real materials, however, is lacking because the pristine Mott state is commonly obscured by antiferromagnetism and a complicated band structure. Here we study organic quantum spin liquids, prototype realizations of the single-band Hubbard model in the absence of magnetic order. Mapping the Hubbard bands by optical spectroscopy provides an absolute measure of the interaction strength and bandwidth-the crucial parameters that enter calculations. In this way, we advance beyond conventional temperature-pressure plots and quantitatively compose a generic phase diagram for all genuine Mott insulators based on the absolute strength of the electronic correlations. We also identify metallic quantum fluctuations as a precursor of the Mott insulator-metal transition, previously predicted but never observed. Our results suggest that all relevant phenomena in the phase diagram scale with the Coulomb repulsion U, which provides a direct link to unconventional superconductivity in cuprates and other strongly correlated materials.
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Affiliation(s)
- A Pustogow
- Physikalisches Institut, Universität Stuttgart, Stuttgart, Germany.
| | - M Bories
- Physikalisches Institut, Universität Stuttgart, Stuttgart, Germany
| | - A Löhle
- Physikalisches Institut, Universität Stuttgart, Stuttgart, Germany
| | - R Rösslhuber
- Physikalisches Institut, Universität Stuttgart, Stuttgart, Germany
| | - E Zhukova
- Moscow Institute of Physics and Technology (State University), Dolgoprudny, Russia
| | - B Gorshunov
- Moscow Institute of Physics and Technology (State University), Dolgoprudny, Russia
| | - S Tomić
- Institut za fiziku, Zagreb, Croatia
| | - J A Schlueter
- Division of Materials Research, National Science Foundation, Arlington, VA, USA
- Materials Science Division, Argonne National Laboratory, Argonne, IL, USA
| | - R Hübner
- Physikalisches Institut, Universität Stuttgart, Stuttgart, Germany
- Biomedizinische Chemie, Institut für Klinische Radiologie und Nuklearmedizin, Universität Heidelberg, Mannheim, Germany
| | - T Hiramatsu
- Faculty of Agriculture, Meijo University, Nagoya, Japan
| | - Y Yoshida
- Faculty of Agriculture, Meijo University, Nagoya, Japan
- Division of Chemistry, Graduate School of Science, Kyoto University, Kyoto, Japan
| | - G Saito
- Faculty of Agriculture, Meijo University, Nagoya, Japan
- Toyota Physical and Chemical Research Institute, Nagakute, Japan
| | - R Kato
- Condensed Molecular Materials Laboratory, RIKEN, Wako-shi, Saitama, Japan
| | - T-H Lee
- Department of Physics and National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, USA
| | - V Dobrosavljević
- Department of Physics and National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, USA
| | - S Fratini
- Institut Néel - CNRS and Université Grenoble Alpes, Grenoble, France
| | - M Dressel
- Physikalisches Institut, Universität Stuttgart, Stuttgart, Germany
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Pustogow A, Saito Y, Zhukova E, Gorshunov B, Kato R, Lee TH, Fratini S, Dobrosavljević V, Dressel M. Low-Energy Excitations in Quantum Spin Liquids Identified by Optical Spectroscopy. Phys Rev Lett 2018; 121:056402. [PMID: 30118313 DOI: 10.1103/physrevlett.121.056402] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2018] [Indexed: 06/08/2023]
Abstract
The electrodynamic response of organic spin liquids with highly frustrated triangular lattices has been measured in a wide energy range. While the overall optical spectra of these Mott insulators are governed by transitions between the Hubbard bands, distinct in-gap excitations can be identified at low temperatures and frequencies, which we attribute to the quantum-spin-liquid state. For the strongly correlated β^{'}-EtMe_{3}Sb[Pd(dmit)_{2}]_{2}, we discover enhanced conductivity below 175 cm^{-1}, comparable to the energy of the magnetic coupling J≈250 K. For ω→0, these low-frequency excitations vanish faster than the charge-carrier response subject to Mott-Hubbard correlations, resulting in a dome-shaped band peaked at 100 cm^{-1}. Possible relations to spinons, magnons, and disorder are discussed.
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Affiliation(s)
- A Pustogow
- 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart, Germany
| | - Y Saito
- 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart, Germany
- Department of Physics, Hokkaido University, Sapporo 060-0810, Japan
| | - E Zhukova
- Moscow Institute of Physics and Technology (State University), 141700, Dolgoprudny, Moscow Region, Russia
| | - B Gorshunov
- Moscow Institute of Physics and Technology (State University), 141700, Dolgoprudny, Moscow Region, Russia
| | - R Kato
- Condensed Molecular Materials Laboratory, RIKEN, Wako-shi, Saitama 351-0198, Japan
| | - T-H Lee
- Department of Physics and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306, USA
| | - S Fratini
- Institut Néel-CNRS and Université Grenoble Alpes, 38042 Grenoble Cedex 9, France
| | - V Dobrosavljević
- Department of Physics and National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32306, USA
| | - M Dressel
- 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70550 Stuttgart, Germany
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