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Wakamatsu K, Suzuki Y, Fujii T, Miyagawa K, Taniguchi H, Kanoda K. Thermoelectric signature of quantum critical phase in a doped spin-liquid candidate. Nat Commun 2023; 14:3679. [PMID: 37344458 DOI: 10.1038/s41467-023-39217-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2022] [Accepted: 05/31/2023] [Indexed: 06/23/2023] Open
Abstract
Quantum spin liquid is a nontrivial magnetic state of longstanding interest, in which spins are strongly correlated and entangled but do not order; further intriguing is its doped version, which possibly hosts strange metal and unconventional superconductivity. A promising candidate of the doped spin liquid is a triangular-lattice organic conductor, κ-(BEDT-TTF)4Hg2.89Br8, recently found to hold metallicity, spin-liquid-like magnetism, and BEC-like superconductivity. The nature of the metallic state with the spin-liquid behaviour is awaiting to be further clarified. Here, we report the thermoelectric signature that mobile holes in the spin liquid background are in a quantum critical state and it pertains to the BEC-like superconductivity. The Seebeck coefficient divided by temperature, S/T, is enhanced on cooling with logarithmic divergence indicative of quantum criticality. Furthermore, the logarithmic enhancement is correlated with the superconducting transition temperature under pressure variation, and the temperature and magnetic field profile of S/T upon the superconducting transition change with pressure in a consistent way with the previously suggested BEC-BCS crossover. The present results reveal that the quantum criticality in a doped spin liquid emerges in a phase, not at a point, and is involved in the unconventional BEC-like nature.
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Affiliation(s)
- K Wakamatsu
- Department of Applied Physics, University of Tokyo; Bunkyo-ku, Tokyo, 113-8656, Japan
| | - Y Suzuki
- Department of Applied Physics, University of Tokyo; Bunkyo-ku, Tokyo, 113-8656, Japan
| | - T Fujii
- Cryogenic Research Center, University of Tokyo; Bunkyo-ku, Tokyo, 113-0032, Japan
| | - K Miyagawa
- Department of Applied Physics, University of Tokyo; Bunkyo-ku, Tokyo, 113-8656, Japan
| | - H Taniguchi
- Graduate School of Science and Engineering, Saitama University, Saitama, 338-8570, Japan
| | - K Kanoda
- Department of Applied Physics, University of Tokyo; Bunkyo-ku, Tokyo, 113-8656, Japan.
- Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569, Stuttgart, Germany.
- Physics Institute, University of Stuttgart, Pfaffenwaldring 57, D-70569, Stuttgart, Germany.
- Department of Advanced Materials Science, University of Tokyo, Kashiwanoha 5-1-5, Kashiwa, 277-8561, Chiba, Japan.
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Matsuura K, Nishizawa Y, Kriener M, Kurumaji T, Oike H, Tokura Y, Kagawa F. Thermodynamic determination of the equilibrium first-order phase-transition line hidden by hysteresis in a phase diagram. Sci Rep 2023; 13:6876. [PMID: 37106004 PMCID: PMC10140377 DOI: 10.1038/s41598-023-33816-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2023] [Accepted: 04/19/2023] [Indexed: 04/29/2023] Open
Abstract
In some materials exhibiting field-induced first-order transitions (FOTs), the equilibrium phase-transition line is hidden by the hysteresis region associated with the FOT. In general, phase diagrams form the basis for the study of material science, and the profiles of phase-transition lines separating different thermodynamic phases include comprehensive information about thermodynamic quantities, such as latent heat. However, in a field-induced FOT, the equilibrium phase-transition line cannot be precisely determined from measurements of resistivity, magnetization, etc, especially when the transition is accompanied by large hysteresis. Here, we demonstrate a thermodynamics-based method for determining the hidden equilibrium FOT line in a material exhibiting a field-induced FOT. This method is verified for the field-induced FOT between antiferromagnetic and ferrimagnetic states in magneto-electric compounds ([Formula: see text]. The equilibrium FOT line determined based on the Clausius-Clapeyron equation exhibits a reasonable profile in terms of the third law of thermodynamics, and it shows marked differences from the midpoints of the hysteresis region. Our findings highlight that for a field-induced FOT exhibiting large hysteresis, care should be taken for referring to the hysteresis midpoint line when discussing field-induced latent heat or magnetocaloric effects.
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Affiliation(s)
- Keisuke Matsuura
- RIKEN Center for Emergent Matter Science, Wako, 351-0198, Japan.
| | - Yo Nishizawa
- Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Tokyo, 113-8656, Japan
| | - Markus Kriener
- RIKEN Center for Emergent Matter Science, Wako, 351-0198, Japan
| | - Takashi Kurumaji
- Department of Advanced Materials Science, University of Tokyo, Kashiwa, 277-8561, Japan
| | - Hiroshi Oike
- RIKEN Center for Emergent Matter Science, Wako, 351-0198, Japan
- Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Tokyo, 113-8656, Japan
- PRESTO, Japan Science and Technology Agency (JST), Kawaguchi, 332-0012, Japan
| | - Yoshinori Tokura
- RIKEN Center for Emergent Matter Science, Wako, 351-0198, Japan
- Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Tokyo, 113-8656, Japan
- Tokyo College, University of Tokyo, Tokyo, 113-8656, Japan
| | - Fumitaka Kagawa
- RIKEN Center for Emergent Matter Science, Wako, 351-0198, Japan
- Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Tokyo, 113-8656, Japan
- Department of Physics, Tokyo Institute of Technology, Tokyo, 152-8551, Japan
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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] [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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Pressure-Tuned Superconducting Dome in Chemically-Substituted κ-(BEDT-TTF)2Cu2(CN)3. CRYSTALS 2021. [DOI: 10.3390/cryst11070817] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The quantum spin liquid candidate κ-(BEDT-TTF)2Cu2(CN)3 has been established as the prime example of a genuine Mott insulator that can be tuned across the first-order insulator–metal transition either by chemical substitution or by physical pressure. Here, we explore the superconducting state that occurs at low temperatures, when both methods are combined, i.e., when κ-[(BEDT-TTF)1−x(BEDT-STF)x]2Cu2(CN)3 is pressurized. We discovered superconductivity for partial BEDT-STF substitution with x = 0.10–0.12 even at ambient pressure, i.e., a superconducting state is realized in the range between a metal and a Mott insulator without magnetic order. Furthermore, we observed the formation of a superconducting dome by pressurizing the substituted crystals; we assigned this novel behavior to disorder emanating from chemical tuning.
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Pustogow A, Saito Y, Löhle A, Sanz Alonso M, Kawamoto A, Dobrosavljević V, Dressel M, Fratini S. Rise and fall of Landau's quasiparticles while approaching the Mott transition. Nat Commun 2021; 12:1571. [PMID: 33692366 PMCID: PMC7977040 DOI: 10.1038/s41467-021-21741-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2020] [Accepted: 02/08/2021] [Indexed: 11/09/2022] Open
Abstract
Landau suggested that the low-temperature properties of metals can be understood in terms of long-lived quasiparticles with all complex interactions included in Fermi-liquid parameters, such as the effective mass m⋆. Despite its wide applicability, electronic transport in bad or strange metals and unconventional superconductors is controversially discussed towards a possible collapse of the quasiparticle concept. Here we explore the electrodynamic response of correlated metals at half filling for varying correlation strength upon approaching a Mott insulator. We reveal persistent Fermi-liquid behavior with pronounced quadratic dependences of the optical scattering rate on temperature and frequency, along with a puzzling elastic contribution to relaxation. The strong increase of the resistivity beyond the Ioffe–Regel–Mott limit is accompanied by a ‘displaced Drude peak’ in the optical conductivity. Our results, supported by a theoretical model for the optical response, demonstrate the emergence of a bad metal from resilient quasiparticles that are subject to dynamical localization and dissolve near the Mott transition. Charge transport in strongly correlated electron systems is not fully understood. Here, the authors show that resilient quasiparticles at finite frequency persist into the bad-metal regime near a Mott insulator, where dynamical localization results in a ‘displaced Drude peak’ and strongly enhanced dc resistivity.
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Affiliation(s)
- Andrej Pustogow
- 1. Physikalisches Institut, Universität Stuttgart, 70569, Stuttgart, Germany. .,Department of Physics and Astronomy, UCLA, Los Angeles, CA, USA. .,Institute of Solid State Physics, Vienna University of Technology, Vienna, Austria.
| | - Yohei Saito
- 1. Physikalisches Institut, Universität Stuttgart, 70569, Stuttgart, Germany.,Department of Physics, Graduate School of Science, Hokkaido University, Sapporo, Japan
| | - Anja Löhle
- 1. Physikalisches Institut, Universität Stuttgart, 70569, Stuttgart, Germany
| | - Miriam Sanz Alonso
- 1. Physikalisches Institut, Universität Stuttgart, 70569, Stuttgart, Germany
| | - Atsushi Kawamoto
- Department of Physics, Graduate School of Science, Hokkaido University, Sapporo, Japan
| | - Vladimir Dobrosavljević
- Department of Physics and National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, USA
| | - Martin Dressel
- 1. Physikalisches Institut, Universität Stuttgart, 70569, Stuttgart, Germany.
| | - Simone Fratini
- Institut Néel - CNRS and Université Grenoble Alpes, Grenoble Cedex 9, France.
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Song M, Xian C, Wang Y, Song J, Li Z, Ling L, Zhang L, Han Y, Cao L, Xiong Y. Disorder-driven non-Fermi liquid behavior in itinerant ferromagnet α-Co 5Ge 3. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2020; 32:155802. [PMID: 31846939 DOI: 10.1088/1361-648x/ab62be] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
The physical properties of itinerant ferromagnet [Formula: see text]-Co5Ge3 with both strong disorder and spin fluctuations was studied. The dc and ac susceptibility show that both spin fluctuations and disorder dominate the physical properties. In the spin glass phase, with a coexisting ferromagnetic state ([Formula: see text]30 K), both non-Fermi liquid behavior and large exponent of scaling relation of [Formula: see text] are observed and attributed to the spin fluctuations and disorder induced by cobalt defects. Upon the increase of external field, Fermi liquid behavior restores due to the suppression of spin fluctuations and disorder. In addition, a large anomalous Hall coefficient R s is observed. Our results suggest that [Formula: see text]-Co5Ge3 is a typical itinerant ferromagnet to explore the interplay of disorder and spin fluctuations.
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Affiliation(s)
- Meng Song
- Anhui Province Key Laboratory of Condensed Matter Physics at Extreme Conditions, High Magnetic Field Laboratory of the Chinese Academy of Sciences, Hefei, Anhui 230031, People's Republic of China. University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China
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Walsh C, Sémon P, Poulin D, Sordi G, Tremblay AMS. Local Entanglement Entropy and Mutual Information across the Mott Transition in the Two-Dimensional Hubbard Model. PHYSICAL REVIEW LETTERS 2019; 122:067203. [PMID: 30822052 DOI: 10.1103/physrevlett.122.067203] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2018] [Indexed: 06/09/2023]
Abstract
Entanglement and information are powerful lenses to probe phases transitions in many-body systems. Motivated by recent cold atom experiments, which are now able to measure the corresponding information-theoretic quantities, we study the Mott transition in the half-filled two-dimensional Hubbard model using cellular dynamical mean-field theory, and focus on two key measures of quantum correlations: entanglement entropy and a measure of total mutual information. We show that they detect the first-order nature of the transition, the universality class of the end point, and the crossover emanating from the end point.
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Affiliation(s)
- C Walsh
- Department of Physics, Royal Holloway, University of London, Egham, Surrey, United Kingdom, TW20 0EX
| | - P Sémon
- Computational Science Initiative, Brookhaven National Laboratory, Upton, New York 11973-5000, USA
| | - D Poulin
- Département de physique & Institut quantique, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1
- Canadian Institute for Advanced Research, Toronto, Ontario, Canada, M5G 1Z8
| | - G Sordi
- Department of Physics, Royal Holloway, University of London, Egham, Surrey, United Kingdom, TW20 0EX
| | - A-M S Tremblay
- Département de physique & Institut quantique, Université de Sherbrooke, Sherbrooke, Québec, Canada J1K 2R1
- Canadian Institute for Advanced Research, Toronto, Ontario, Canada, M5G 1Z8
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Rösslhuber R, Uykur E, Dressel M. Pressure cell for radio-frequency dielectric measurements at low temperatures. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2018; 89:054708. [PMID: 29864800 DOI: 10.1063/1.5030847] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We present the design, test, and performance of a piston type pressure cell for low-temperature dielectric measurements up to 10 kbar with particular emphasis on the electrical feedthrough for four coaxial cables and four conventional copper wires. The coaxial cables provide proper shielding of the applied test signal; a commercial continuous flow cryostat allows us to minimize the total cable length enabling temperature and pressure-dependent dielectric spectroscopy measurements down to 8 K and up to 5 MHz. We performed open compensation measurements, i.e., background measurements of the response originating from the pressure setup without a sample, to obtain its high frequency characteristics. The stray capacitance of the pressure setup is determined as Cstray = 40 fF, making it possible to measure small single crystals with a weak dielectric response. The proper operation is verified by comparing measurements of a test sample in the pressure setup at ambient pressure and in a standard dielectric spectroscopy setup.
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Affiliation(s)
- R Rösslhuber
- 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany
| | - E Uykur
- 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany
| | - M Dressel
- 1. Physikalisches Institut, Universität Stuttgart, Pfaffenwaldring 57, D-70569 Stuttgart, Germany
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