160 results on '"Yasuhiro Nakazawa"'
Search Results
2. Heat capacity of poly(N-vinylpyrrolidone)
- Author
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Kazuhiko Ishikiriyama, Keisuke Kondo, Yuji Miyazaki, Yuto Sasada, Keisuke Sawada, Ryo Endo, Naoki Man, Motohiro Nakano, and Yasuhiro Nakazawa
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Physical and Theoretical Chemistry ,Condensed Matter Physics ,Instrumentation - Published
- 2023
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3. Electric dipole induced bulk ferromagnetism in dimer Mott molecular compounds
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Reizo Kato, Yasuhiro Nakazawa, Hiroki Akutsu, Ryo Yoshimoto, Takehito Nakano, Yugo Oshima, Tetsuro Kusamoto, Hiroshi Yamamoto, and Satoshi Yamashita
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Materials science ,Science ,02 engineering and technology ,Electron ,01 natural sciences ,Article ,Magnetization ,Condensed Matter::Materials Science ,Magnetic properties and materials ,0103 physical sciences ,Antiferromagnetism ,010306 general physics ,Multidisciplinary ,Condensed matter physics ,Mott insulator ,021001 nanoscience & nanotechnology ,Magnetic field ,Dipole ,Ferromagnetism ,Medicine ,Condensed Matter::Strongly Correlated Electrons ,0210 nano-technology ,Ground state - Abstract
Magnetic properties of Mott–Hubbard systems are generally dominated by strong antiferromagnetic interactions produced by the Coulomb repulsion of electrons. Although theoretical possibility of a ferromagnetic ground state has been suggested by Nagaoka and Penn as single-hole doping in a Mott insulator, experimental realization has not been reported more than half century. We report the first experimental possibility of such ferromagnetism in a molecular Mott insulator with an extremely light and homogeneous hole-doping in π-electron layers induced by net polarization of counterions. A series of Ni(dmit)2 anion radical salts with organic cations, where dmit is 1,3-dithiole-2-thione-4,5-dithiolate can form bi-layer structure with polarized cation layers. Heat capacity, magnetization, and ESR measurements substantiated the formation of a bulk ferromagnetic state around 1.0 K with quite soft magnetization versus magnetic field (M–H) characteristics in (Et-4BrT)[Ni(dmit)2]2 where Et-4BrT is ethyl-4-bromothiazolium. The variation of the magnitude of net polarizations by using the difference of counter cations revealed the systematic change of the ground state from antiferromagnetic one to ferromagnetic one. We also report emergence of metallic states through further doping and applying external pressures for this doping induced ferromagnetic state. The realization of ferromagnetic state in Nagaoka–Penn mechanism can paves a way for designing new molecules-based ferromagnets in future.
- Published
- 2021
4. Structural, magnetic and Mössbauer spectroscopic studies of the [Fe(3-bpp)2](CF3COO)2 complex: role of crystal packing leading to an incomplete Fe(<scp>ii</scp>) high spin ⇋ low spin transition
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Djulia Onggo, Varimalla Raghavendra Reddy, Hiroki Akutsu, Ashis Bhattacharjee, Yasuhiro Nakazawa, Hari Sutrisno, and Kristian Handoyo Sugiyarto
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Diffraction ,Materials science ,Transition temperature ,Spin transition ,General Chemistry ,Condensed Matter Physics ,Crystal ,chemistry.chemical_compound ,Crystallography ,chemistry ,Mössbauer spectroscopy ,Pyridine ,General Materials Science ,Single crystal ,Spin-½ - Abstract
Single crystal X-ray diffraction, magnetic and 57Fe Mossbauer spectroscopic studies of a new iron(II)-based spin transition complex – [Fe(3-bpp)2](CF3COO)2 (bpp = 2,6-bis(pyrazol-3-yl)pyridine) are reported. The complex exhibits an incomplete thermal high spin (HS) low spin (LS) transition at ∼226 K which is not associated with any crystallographic transition. Only one of the two crystallographic iron(II) sites undergoes the spin transition, while the other HS site remains invariant of temperature down to 10 K. The origin of the incomplete spin transition is understood by analysing the nature of crystal packing below and above the transition temperature with special attention to the degree of distortion. The present study shows the role of the degree of distortion associated with the cations in the [Fe(3-bpp)2]2+ spin transition complexes.
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- 2021
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5. Chiral molecular conductor with an insulator–metal transition close to room temperature
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Hiroki Akutsu, Jonathan I Short, Songjie Yang, Toby J. Blundell, Yasuhiro Nakazawa, Lee Martin, John D. Wallis, and Sara J. Krivickas
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Materials science ,Condensed matter physics ,Metals and Alloys ,Insulator (electricity) ,General Chemistry ,Conductivity ,Catalysis ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Conductor ,Metal ,visual_art ,Materials Chemistry ,Ceramics and Composites ,visual_art.visual_art_medium ,Chirality (chemistry) - Abstract
Materials exhibiting both chirality and conductivity do not exist in nature and very few examples have been synthesised. We report here the synthesis of a chiral molecular metal which remains metallic down to at least 4.2 K. This material also exhibits room-temperature switching capabilities with a transition upon cooling below 10 °C.
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- 2020
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6. Electronic Heat Capacity and Lattice Softening of Partially Deuterated Compounds of κ-(BEDT-TTF)2Cu[N(CN)2]Br
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Yuki Matsumura, Shusaku Imajo, Satoshi Yamashita, Hiroki Akutsu, and Yasuhiro Nakazawa
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Inorganic Chemistry ,heat capacity ,Crystallography ,strong electron correlations ,Mott transition ,QD901-999 ,General Chemical Engineering ,organic superconductor ,General Materials Science ,Condensed Matter Physics - Abstract
Thermodynamic investigation by calorimetric measurements of the layered organic superconductors, κ-(BEDT-TTF)2Cu[N(CN)2]Br and its partially deuterated compounds of κ-(d[2,2]-BEDT-TTF)2Cu[N(CN)2]Br and κ-(d[3,3]-BEDT-TTF)2Cu[N(CN)2]Br, performed in a wide temperature range is reported. The latter two compounds were located near the metal–insulator boundary in the dimer-Mott phase diagram. From the comparison of the temperature dependences of their heat capacities, we indicated that lattice heat capacities of the partially deuterated compounds were larger than that of the pristine compound below about 40 K. This feature probably related to the lattice softening was discussed also by the sound velocity measurement, in which the dip-like structures of the Δv/v were observed. We also discussed the variation of the electronic heat capacity under magnetic fields. From the heat capacity data at magnetic fields up to 6 T, we evaluated that the normal-state γ value of the partially deuterated compound, κ-(d[3,3]-BEDT-TTF)2Cu[N(CN)2]Br, was about 3.1 mJ K−2 mol−1. Under the magnetic fields higher than 3.0 T, we observed that the magnetic-field insulating state was induced due to the instability of the mid-gap electronic state peculiar for the two-dimensional dimer-Mott system. Even though the volume fraction was much reduced, the heat capacity of κ-(d[3,3]-BEDT-TTF)2Cu[N(CN)2]Br showed a small hump structure probably related to the strong coupling feature of the superconductivity near the boundary.
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- 2021
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7. Fermi Surface Structure and Isotropic Stability of Fulde-Ferrell-Larkin-Ovchinnikov Phase in Layered Organic Superconductor β″-(BEDT-TTF)2SF5CH2CF2SO3
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Shiori Sugiura, Hiroki Akutsu, Yasuhiro Nakazawa, Taichi Terashima, Syuma Yasuzuka, John A. Schlueter, and Shinya Uji
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Condensed Matter::Quantum Gases ,Crystallography ,General Chemical Engineering ,FFLO phase ,MathematicsofComputing_GENERAL ,organic superconductor ,Condensed Matter Physics ,vortex dynamics ,Inorganic Chemistry ,resistance ,TheoryofComputation_MATHEMATICALLOGICANDFORMALLANGUAGES ,QD901-999 ,Condensed Matter::Superconductivity ,Condensed Matter::Strongly Correlated Electrons ,General Materials Science - Abstract
The Fermi surface structure of a layered organic superconductor β″-(BEDT-TTF)2SF5CH2CF2SO3 was determined by angular-dependent magnetoresistance oscillations measurements and band-structure calculations. This salt was found to have two small pockets with the same area: a deformed square hole pocket and an elliptic electron pocket. Characteristic corrugations in the field dependence of the interlayer resistance in the superconducting phase were observed at any in-plane field directions. The features were ascribed to the commensurability (CM) effect between the Josephson vortex lattice and the periodic nodal structure of the superconducting gap in the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase. The CM effect was observed in a similar field region for various in-plane field directions, in spite of the anisotropic nature of the Fermi surface. The results clearly showed that the FFLO phase stability is insensitive to the in-plane field directions.
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- 2021
8. Extraordinary $\pi$-Electron Superconductivity Emerging from a Quantum Spin Liquid
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Yoshimitsu Kohama, Taichi Terashima, Hiroki Akutsu, Shusaku Imajo, S. Uji, Shiori Sugiura, Yasuhiro Nakazawa, Takayuki Isono, and K. Kindo
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Superconductivity ,Physics ,Condensed Matter - Materials Science ,Condensed matter physics ,Spins ,Condensed Matter - Superconductivity ,Doping ,Electron ,Condensed Matter - Strongly Correlated Electrons ,Metallic conductivity ,Condensed Matter::Superconductivity ,Hexagonal lattice ,Condensed Matter::Strongly Correlated Electrons ,Quantum spin liquid ,Critical field - Abstract
Quantum spin liquids (QSLs), in which spins are highly entangled, have been considered a groundwork for generating exotic superconductivity. Despite numerous efforts, superconductivity emerging from QSLs has been unrealized in actual materials due to the difficulties in stabilizing QSL states with metallic conductivity. Recently, an organic compound, $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{4}{\mathrm{Hg}}_{2.89}{\mathrm{Br}}_{8}$, with a nearly regular triangular lattice of molecular dimers was recognized as a candidate for doped QSLs. In this study, we report an unusual superconducting phase of $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{4}{\mathrm{Hg}}_{2.89}{\mathrm{Br}}_{8}$: unexpectedly large ratios of the upper critical field to the critical temperature ${H}_{\mathrm{c}2}/{T}_{\mathrm{c}}$ in fields not only parallel but also perpendicular to the two-dimensional conducting layers and a very wide region of fluctuating superconductivity above ${T}_{\mathrm{c}}$. Our results reveal that these peculiarities arise from strong electron correlations and possible quantum criticality unique to the doped QSL state, leading to a heavy mass of itinerant carriers and a large superconducting energy gap.
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- 2021
9. Thermodynamic evidence for the formation of a Fulde-Ferrell-Larkin-Ovchinnikov phase in the organic superconductor λ−(BETS)2GaCl4
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Takuya Kobayashi, Yasuhiro Nakazawa, K. Kindo, Atsushi Kawamoto, and Shusaku Imajo
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Condensed Matter::Quantum Gases ,Superconductivity ,Physics ,Condensed matter physics ,02 engineering and technology ,State (functional analysis) ,021001 nanoscience & nanotechnology ,Lambda ,01 natural sciences ,Fulde–Ferrell–Larkin–Ovchinnikov phase ,symbols.namesake ,Pauli exclusion principle ,Condensed Matter::Superconductivity ,0103 physical sciences ,symbols ,Organic superconductor ,Anomaly (physics) ,010306 general physics ,0210 nano-technology ,Critical field - Abstract
In this work, the thermodynamic properties of the organic superconductor $\ensuremath{\lambda}\text{\ensuremath{-}}{(\mathrm{BETS})}_{2}{\mathrm{GaCl}}_{4}$ are investigated to study a high-field superconducting state known as the putative Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase. We observed a small thermodynamic anomaly in the field ${H}_{\mathrm{FFLO}}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}10$ T, which corresponds to the Pauli limiting field ${H}_{\mathrm{P}}$. This anomaly probably originates from a transition from a uniform superconducting state to the FFLO state. ${H}_{\mathrm{FFLO}}$ does not show a strong-field angular dependence due to a quasi-isotropic paramagnetic effect in $\ensuremath{\lambda}\text{\ensuremath{-}}{(\mathrm{BETS})}_{2}{\mathrm{GaCl}}_{4}$. The thermodynamic anomaly at ${H}_{\mathrm{FFLO}}$ is smeared out. and the low-temperature upper critical field ${H}_{\mathrm{c}2}$ changes significantly if fields are not parallel to the conducting plane, even for a deviation of $\ensuremath{\sim}0.{5}^{\ensuremath{\circ}}$. This behavior indicates that the high-field state is very unstable, as it is influenced by the strongly anisotropic orbital effect. Our results are consistent with the theoretical predictions on the FFLO state and show that the high-field superconductivity is probably an FFLO state in $\ensuremath{\lambda}\text{\ensuremath{-}}{(\mathrm{BETS})}_{2}{\mathrm{GaCl}}_{4}$ from a thermodynamic point of view.
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- 2021
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10. Structures and Properties of New Organic Conductors: BEDT-TTF, BEST and BETS Salts of the HOC2H4SO3− Anion
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Hiroki Akutsu, Yuta Koyama, Keigo Furuta, Scott S. Turner, and Yasuhiro Nakazawa
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Madelung energy ,Materials science ,General Chemical Engineering ,Salt (chemistry) ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Ion ,Inorganic Chemistry ,Metal ,chemistry.chemical_compound ,organic conductors ,Electrical resistivity and conductivity ,bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF) ,bis(ethylenedithio)tetraselenafulvalene (BETS) ,lcsh:QD901-999 ,General Materials Science ,Isostructural ,Electrical conductor ,chemistry.chemical_classification ,bis(ethylenediseleno)tetrathiafulvalene (BEST) ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Magnetic susceptibility ,0104 chemical sciences ,Crystallography ,chemistry ,visual_art ,visual_art.visual_art_medium ,quantum chemical calculations ,lcsh:Crystallography ,charge-ordered state ,0210 nano-technology ,Tetrathiafulvalene ,X-ray analysis ,electrical resistivity ,magnetic susceptibility - Abstract
New bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF)-, bis(ethylenediseleno)tetrathiafulvalene (BEST)- and bis(ethylenedithio)tetraselenafulvalene (BETS)-based organic charge-transfer (CT) salts&mdash, &alpha, (BEDT-TTF)3(HOC2H4SO3)2 (1), &beta, (BEST)3(HOC2H4SO3)2·, H2O (2) and &alpha, (BETS)2(HOC2H4SO3)·, H2O (3)&mdash, have been prepared. Salts 1 and 2 show semiconducting behaviour. Salt 3, which is almost isostructural to &alpha, (BETS)2I3, shows metallic behaviour down to 70 K and then shows a broader metal&ndash, insulator transition than that of &alpha, (BETS)2I3. The reason for the difference in behaviour is estimated by the comparison of the Madelung energies of the full set of patterns of possible donor&rsquo, s charge-ordered and anion&rsquo, s disordered states.
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- 2020
11. Anisotropic Fully-Gapped Superconductivity Possibly Mediated by Charge Fluctuations in a Nondimeric Organic Complex
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Masashi Tokunaga, Hiroki Akutsu, K. Kindo, Takeshi Yajima, Shusaku Imajo, Yoshimitsu Kohama, Yasuhiro Nakazawa, and Ryosuke Kurihara
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Superconductivity ,Physics ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed Matter - Superconductivity ,General Physics and Astronomy ,Quantum oscillations ,FOS: Physical sciences ,Charge (physics) ,Fermi surface ,01 natural sciences ,Heat capacity ,Superconductivity (cond-mat.supr-con) ,Condensed Matter - Strongly Correlated Electrons ,Pairing ,Condensed Matter::Superconductivity ,0103 physical sciences ,Organic superconductor ,010306 general physics ,Anisotropy - Abstract
We investigate low-temperature electronic properties of the nondimeric organic superconductor $\beta^{\prime\prime}$-(BEDT-TTF)$_4$[(H$_3$O)Ga(C$_2$O$_4$)$_3$]PhNO$_2$. By examining ultrasonic properties, charge disproportionation (CD) without magnetic field dependence is detected below $T_{\rm CD}$$\sim$8~K just above the superconducting critical temperature $T_{\rm c}$$\sim$6~K. From quantum oscillations in high fields, we find variation in the Fermi surface and mass enhancement induced by the CD. Heat capacity studies elucidate that the superconducting gap function is fully gapped in the Fermi surface, but anisotropic with fourfold symmetry. We point out that the pairing mechanism of the superconductivity is possibly dominated by charge fluctuations., Comment: 6 figures
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- 2020
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12. Construction of a thermal conductivity measurement system for small single crystals of organic conductors
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Satoshi Yamashita, Yasuhiro Nakazawa, Tetsuya Nomoto, Hiroki Akutsu, Alexander I. Krivchikov, and Shusaku Imajo
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Phase transition ,Materials science ,Drop (liquid) ,Analytical chemistry ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,010406 physical chemistry ,0104 chemical sciences ,Thermal conductivity measurement ,chemistry.chemical_compound ,Thermal conductivity ,chemistry ,Molecule ,Physical and Theoretical Chemistry ,0210 nano-technology ,Electrical conductor ,Tetrathiafulvalene - Abstract
We newly constructed a thermal conductivity measurement system for single crystals of molecular compounds. This system enables us to measure the thermal conductivity of samples with the length of less than 1.0 mm. In order to evaluate the capability of detection of phase transitions occurred in molecule-based materials, we performed the thermal conductivity measurement of single crystals of organic conductors α-(BEDT-TTF)2I3 and κ-(BEDT-TTF)2Cu[N(CN)2]Br, where BEDT-TTF denotes bis(ethylenedithio)tetrathiafulvalene. From the temperature dependence of the thermal conductivity of α-(BEDT-TTF)2I3, we succeeded in observing the metal–insulator transition as a sudden drop of κ(T) at 135 K. In the temperature dependence of thermal conductivity of κ-(BEDT-TTF)2Cu[N(CN)2]Br, we could observe the increment of κ(T) at the metal-superconducting transition (Tc = 11.4 K). These results show that the newly developed system has high performance enough to detect various kinds of phase transitions in small crystals of molecular compounds.
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- 2018
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13. AC calorimetry system using commercially available microchip device and its application for tiny single crystals of molecule-based compounds
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Shusaku Imajo, Reizo Kato, Satoshi Yamashita, Yasuhiro Nakazawa, Kohei Ueda, Michinori Murase, and Ryo Yoshimoto
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Chemistry ,Relaxation (NMR) ,Analytical chemistry ,02 engineering and technology ,Calorimetry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Charge-transfer complex ,01 natural sciences ,Heat capacity ,0104 chemical sciences ,Crystal ,Molecule ,Physical and Theoretical Chemistry ,Quantum spin liquid ,0210 nano-technology ,Instrumentation ,Single crystal - Abstract
The constructional details and performance of a low-temperature ac calorimetric system for extremely small single crystal samples of molecule-based compounds of which sensing parts is consisting of commercially available micro-chip device of XEN-39390 are reported. We succeeded to detect the thermal anomaly related to the glass formation of the ethylene conformation in a charge transfer complex of κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br, where BEDT-TTF is bisethylenedithiotetrathiafulvalene. From the analyses of temperature and frequency dependences of heat capacity, we suggest that XEN-39390 can give similar experimental resolution as that of TCG-3880 with much smaller single crystals less than 100 ng. We also observed a glass-like freezing of molecular dynamics in the large asymmetric cations in EtMe 3 Sb[Pd(dmit) 2 ] 2 which are known as a spin liquid compound by single piece of crystal where dmit is 1,3-dithiole-2-thione-4,5-dithiolate. The comparison with the relaxation calorimetry result with absolute precision is performed.
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- 2017
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14. Magnetic and Electronic Properties of π-d Interacting Molecular Magnetic Superconductor κ-(BETS)2FeX4 (X = Cl, Br) Studied by Angle-Resolved Heat Capacity Measurements
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Hiroki Akutsu, Shuhei Fukuoka, Sotarou Fukuchi, Yasuhiro Nakazawa, and Atsushi Kawamoto
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Materials science ,General Chemical Engineering ,magnetic conductor ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Heat capacity ,Inorganic Chemistry ,single crystal heat capacity measurement ,lcsh:QD901-999 ,Antiferromagnetism ,General Materials Science ,Anisotropy ,Superconductivity ,thermodynamic measurement ,Condensed matter physics ,Transition temperature ,superconductivity ,π-d system ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,0104 chemical sciences ,Magnetic field ,Magnetic anisotropy ,Magnet ,antiferromagnetism ,lcsh:Crystallography ,0210 nano-technology - Abstract
Thermodynamic picture induced by π-d interaction in a molecular magnetic superconductor κ-(BETS)2FeX4 (X = Cl, Br), where BETS is bis(ethylenedithio)tetraselenafulvalene, studied by single crystal calorimetry is reviewed. Although the S = 5/2 spins of Fe3+ in the anion layers form a three-dimensional long-range ordering with nearly full entropy of Rln6, a broad hump structure appears in the temperature dependence of the magnetic heat capacity only when the magnetic field is applied parallel to the a axis, which is considered as the magnetic easy axis. The scaling of the temperature dependence of the magnetic heat capacity of the two salts is possible using the parameter of |Jdd|/kB and therefore the origin of the hump structure is related to the direct magnetic interaction, Jdd, that is dominant in the system. Quite unusual crossover from a three-dimensional ordering to a one-dimensional magnet occurs when magnetic fields are applied parallel to the a axis. A notable anisotropic field-direction dependence against the in-plane magnetic field was also observed in the transition temperature of the bulk superconductivity by the angle-resolved heat capacity measurements. We discuss the origin of this in-plane anisotropy in terms of the 3d electron spin configuration change induced by magnetic fields.
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- 2019
15. Lattice and Charge Fluctuations in a Molecular Superconductor
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Hiroki Akutsu, Toshio Naito, Mikio Uruichi, Yasuhiro Nakazawa, and Takashi Yamamoto
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Superconductivity ,Lattice (module) ,symbols.namesake ,Materials science ,Condensed matter physics ,Condensed Matter::Superconductivity ,symbols ,General Physics and Astronomy ,Superconducting transition temperature ,Condensed Matter::Strongly Correlated Electrons ,Charge (physics) ,Raman spectroscopy ,Astrophysics::Galaxy Astrophysics - Abstract
We report IR and Raman spectra for a two-dimensional superconductor, β′′-(BEDT-TTF)4[Ga(C2O4)3(H3O)]C6H5NO2, below the superconducting transition temperature. The behavior of the lattice-sensitive ...
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- 2021
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16. Molecular beam deposition of a new layered pnictide with distorted Sb square nets
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Yasuhiro Nakazawa, Masashi Tokunaga, Masaki Uchida, Atsushi Miyake, Masashi Kawasaki, Mizuki Ohno, Sota Sato, Markus Kriener, and Yasujiro Taguchi
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Materials science ,QC1-999 ,Dirac (software) ,FOS: Physical sciences ,02 engineering and technology ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,Transition metal ,0103 physical sciences ,Antiferromagnetism ,General Materials Science ,Thin film ,Pnictogen ,010302 applied physics ,Condensed Matter - Materials Science ,Ionic radius ,Strongly Correlated Electrons (cond-mat.str-el) ,Magnetic moment ,Condensed matter physics ,Physics ,General Engineering ,Materials Science (cond-mat.mtrl-sci) ,021001 nanoscience & nanotechnology ,Orthorhombic crystal system ,0210 nano-technology ,TP248.13-248.65 ,Biotechnology - Abstract
While the family of layered pnictides $ABX_2$ ($A$ : rare or alkaline earth metals, $B$ : transition metals, $X$ : Sb/Bi) can host Dirac dispersions based on Sb/Bi square nets, nearly half of them has not been synthesized yet for possible combinations of the $A$ and $B$ cations. Here we report the fabrication of EuCdSb$_{\mathrm{2}}$ with the largest $B$-site ionic radius, which is stabilized for the first time in thin film form by molecular beam deposition. EuCdSb$_{\mathrm{2}}$ crystallizes in an orthorhombic $Pnma$ structure and exhibits antiferromagnetic ordering of the Eu magnetic moments at $T_\mathrm{N}=15$K. Our successful growth will be an important step for further exploring novel Dirac materials using film techniques., 12 pages, 4 figures
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- 2021
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17. Magnetic Properties of S = 1/2 Distorted Kagome Antiferromagnet CdCu3(OH)6Cl2 with Low-Symmetry Orbital Arrangement
- Author
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Yasuo Narumi, Yuto Ishii, Satoshi Yamashita, Kazunari Yamaura, Masayuki Hagiwara, Takanori Kida, Hiroyuki Yoshida, Jie Chen, Migaku Oda, Naoya Noguchi, and Yasuhiro Nakazawa
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Magnetization ,Materials science ,Condensed matter physics ,General Physics and Astronomy ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Low symmetry ,Magnetic susceptibility ,Heat capacity - Abstract
The magnetic properties of the S = 1/2 distorted kagome antiferromagnet CdCu3(OH)6Cl2 have been studied by magnetic susceptibility, heat capacity, and high-field magnetization measurements. The mag...
- Published
- 2021
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18. Magnetocaloric effect of high-spin cluster with Ni9W6 core
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Beata Nowicka, Barbara Sieklucka, Mateusz Reczyński, Yuji Miyazaki, Magdalena Fitta, Yasuhiro Nakazawa, Robert Pełka, M. Gajewski, and Maria Bałanda
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Materials science ,Condensed matter physics ,Demagnetizing field ,Analytical chemistry ,Field dependence ,02 engineering and technology ,Calorimetry ,Triclinic crystal system ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Heat capacity ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Magnetic refrigeration ,0210 nano-technology ,Anisotropy ,Adiabatic process - Abstract
A study of magnetocaloric effect of a structurally unique molecular magnet built of spin clusters with the pentadecanuclear Ni(II) 9 W(V) 6 core forming a cube-like framework is reported. The compound crystallizes in the triclinic system. The clusters display anisotropy quantified with the axial D =0.07 K and rhombic E =0.023 K anisotropy constants. The temperature dependences of magnetic entropy change Δ S M as well as the adiabatic temperature change Δ T ad due to applied field change μ 0 Δ H ranging from 1 to 9 T have been determined by employing the relaxation calorimetry measurements in applied field. The maximum value of Δ S M for μ 0 Δ H =5 T is 18.38 J K −1 mol −1 (3.36 J K −1 kg −1 ) at 4.3 K. The corresponding maximum value of Δ T ad =4.6 K is attained at 2.2 K. The occurrence of the inverse MCE has been observed at high temperatures for small field change values. The temperature dependence of the exponent n characterizing the field dependence of Δ S M has been estimated and discussed. The study revealed that the compound may be treated as a possible candidate for cryogenic magnetic cooling.
- Published
- 2016
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19. Thermal anomaly around the superconductive transition of κ-(BEDT-TTF)2Cu(NCS)2 with external pressure and magnetic field control
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Shusaku Imajo, Yuki Muraoka, Satoshi Yamashita, Yasuhiro Nakazawa, and Hiroki Akutsu
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Superconductivity ,Condensed matter physics ,Chemistry ,Transition temperature ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Heat capacity ,Magnetic field ,Condensed Matter::Superconductivity ,Phase (matter) ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,Physical and Theoretical Chemistry ,Anomaly (physics) ,010306 general physics ,0210 nano-technology ,Ambient pressure ,Phase diagram - Abstract
The temperature dependence of the ac heat capacity of a molecule-based superconductor κ-(BEDT-TTF)2Cu(NCS)2 under external pressures and with magnetic fields is reported. A peak structure in C p T −1 due to the superconductive transition was observed around 9 K at ambient pressure. This peak is suppressed by applying magnetic fields up to 7 T. The systematic decrease in the transition temperature with the increase in external pressure is confirmed by thermodynamic measurements under 0.15, 0.30 and 0.45 GPa. Through the analysis of the peak shape of the thermal anomaly, it is suggested that the gradual suppression of the coupling strength of the superconductivity occurs with the increase in pressure. This feature is consistent with the argument based on the chemical pressure effect in the superconductive phase of κ-(BEDT-TTF)2 X system, where X denotes mono-valence counter anions. The result demonstrates that the appearance of the Fermi-liquid character produced by applying pressure in the dimer-Mott phase diagram affects the nature and the coupling feature of the superconductivity. Importance of high-pressure heat capacity for molecule-based compounds is emphasized.
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- 2016
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20. Single Crystal Heat Capacity Measurement of Charge Glass Compound θ-(BEDT-TTF)2CsZn(SCN)4 Performed under Current and Voltage Application
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Kosei Hino, Tetsuya Nomoto, Satoshi Yamashita, and Yasuhiro Nakazawa
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heat capacity ,Materials science ,General Chemical Engineering ,electric voltage ,02 engineering and technology ,Calorimetry ,01 natural sciences ,Heat capacity ,Inorganic Chemistry ,Electrical resistivity and conductivity ,0103 physical sciences ,lcsh:QD901-999 ,General Materials Science ,010306 general physics ,Boson peak ,Computer Science::Information Theory ,electric current ,Condensed matter physics ,Charge density ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Relaxation (physics) ,lcsh:Crystallography ,charge glass ,Electric current ,0210 nano-technology ,Ground state ,Joule heating - Abstract
Heat capacity measurements of &theta, (BEDT-TTF)2CsZn(SCN)4 in its non-equilibrium electronic states induced by applying electric currents and voltages were performed by a modified relaxation calorimetry technique. We developed a single crystal heat capacity measurements system by which the Joule heating produced in samples by external currents and voltages can be balanced with the cooling power to make a non-equilibrium steady state. Although temperature versus time profiles in the relaxation process in calorimetry can be obtained as exponential curves as in the usual relaxation technique, we found that the change of resistivity that occurs during the heating and relaxation process should be taken into account in analyzing the data. By correcting this factor in the analyses, we succeeded in evaluating absolute values of Cp(I) and Cp(V) in these non-equilibrium states. The experiments up to 150 &mu, A and the constant voltage of 20 mV do not induce visible change in the structure of the Boson peak in CpT&minus, 3 vs. T suggestive of the glassy ground state of phonons. Although the suppression of the short-range fluctuations of the charge density has been reported, it does not seriously affect the glassy phonons in this current range.
- Published
- 2020
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21. Thermodynamic properties of glassy phonon states induced by strong electron correlations in 𝜃-type organic charge transfer salts
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Yasuhiro Nakazawa, Shinsuke Yamashita, Hiroki Akutsu, Tetsuya Nomoto, and E. Yesil
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chemistry.chemical_classification ,Materials science ,Phonon ,Salt (chemistry) ,Statistical and Nonlinear Physics ,Charge (physics) ,02 engineering and technology ,Electron ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,chemistry ,Chemical physics ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,Boson peak ,010306 general physics ,0210 nano-technology - Abstract
The appearance of electron correlations–induced glassy state of low-energy phonons in the non-dimeric organic charge transfer salt in [Formula: see text]-(BEDT-TTF)2CsZn(SCN)4 is considered as a strong evidence of charge lattice coupling in molecular charge transfer salts. We discuss the temperature and the magnetic field dependences of the heat capacity of this salt in terms of the soft potential model to describe the thermodynamic properties of enhanced phonons that occur in molecular glasses. The evaluated [Formula: see text] term of [Formula: see text]-(BEDT-TTF)2CsZn(SCN)4 is about 30 mJ K[Formula: see text] mol[Formula: see text], which is much larger than other charge transfer salts described by the low-temperature approximation of the Debye model. The magnetic fields dependence of the boson peak is almost negligible, but the low-energy term, for example, in the temperature-linear term of heat capacity shows a slight change, probably due to the small amount of localized spin moments. The comparison with other systems is also performed.
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- 2020
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22. Development of frequency tuning AC modulation method for high-pressure heat capacity measurements of molecules-based compounds
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T. Maruyama, Hiroki Akutsu, Yasuhiro Nakazawa, Tetsuya Nomoto, and Shinsuke Yamashita
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Materials science ,business.industry ,Measure (physics) ,Statistical and Nonlinear Physics ,02 engineering and technology ,Calorimetry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Heat capacity ,Modulation ,High pressure ,0103 physical sciences ,Optoelectronics ,Molecule ,Development (differential geometry) ,Cube ,010306 general physics ,0210 nano-technology ,business - Abstract
The automatic frequency tuning method in the high-pressure ac calorimetry system constructed to measure heat capacity for molecules-based compounds with CuBe[Formula: see text]+[Formula: see text]NiCrAl cramp-type pressure cell is reported. This development is performed for increasing resolution and temperature ranges of the heat capacity measurements under external pressure up to 2.0 GPa. The system can check the appropriate conditions by tracing frequency dependence of [Formula: see text] to determine the oscillation frequency at the center of the plateau region of this value. The experiments using the powder samples of metal complexes clarified that the appropriate frequency changes sensitively depending on the difference of temperature and that of external pressures, especially at low temperature region. It decreases with increasing temperature and this relation was found to be almost linear with temperature in ambient pressure and under pressure conditions. The change of thermal diffusion from the sample part to the heat bath should be treated carefully in order to get enough resolution in high pressure AC heat capacity measurements of molecule-based compounds.
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- 2020
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23. Fulde-Ferrell-Larkin-Ovchinnikov superconductivity in the layered organic superconductor β'−(BEDT−TTF)4[(H3O)Ga(C2O4)3]C6H5NO2
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Kaori Sugii, Taichi Terashima, Naoki Kikugawa, D. Graf, S. Uji, Peter Day, Y. Iida, Syuma Yasuzuka, Yasuhiro Nakazawa, Takayuki Isono, Hiroki Akutsu, and Shiori Sugiura
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Condensed Matter::Quantum Gases ,Superconductivity ,Physics ,Phase transition ,Magnetic moment ,Condensed matter physics ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter::Superconductivity ,0103 physical sciences ,Organic superconductor ,Diamagnetism ,Josephson vortex ,010306 general physics ,0210 nano-technology ,Critical field ,Phase diagram - Abstract
Resistance and magnetic torque measurements are reported in a layered organic superconductor, $\ensuremath{\beta}''\ensuremath{-}{(\mathrm{BEDT}\ensuremath{-}\mathrm{TTF})}_{4}[({\mathrm{H}}_{3}\mathrm{O})\mathrm{Ga}{({\mathrm{C}}_{2}{\mathrm{O}}_{4})}_{3}]{\mathrm{C}}_{6}{\mathrm{H}}_{5}{\mathrm{NO}}_{2}$ with ${T}_{c}=4.8$ K, where BEDT-TTF stands for bis(ethylenedithio)tetrathiafulvalene. Because of the large anion between the BEDT-TTF conducting layers, the superconductivity of this salt is highly anisotropic. In magnetic fields parallel to the conducting layers for $T=0.4$ K, the magnetic torque shows a large diamagnetic signal associated with hysteresis up to $\ensuremath{\sim}21$ T, suggesting the upper critical field ${H}_{c2}\ensuremath{\gtrsim}21$ T at 0.4 K. The large reduction of the diamagnetic signal is observed above 16 T, which shows a Fulde and Ferrell and Larkin and Ovchinnikov (FFLO) phase transition. For $T=0.5$ K, the interlayer resistance has nonzero value in a wide field region up to ${H}_{c2}$, arising from the Josephson vortex dynamics. Successive dips in the second derivative curves of the resistance are observed between 16 T and ${H}_{c2}$, which are ascribed to the commensurability effect between the Josephson vortex lattice and the order parameter oscillation of the FFLO phase. The commensurability effect is observed only in nearly parallel fields, showing that the FFLO phase is stable in a very limited field angle region. The temperature-field phase diagram is determined.
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- 2018
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24. Construction of relaxation calorimetry for 101–2 μg samples and heat capacity measurements of organic complexes
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Shuhei Fukuoka, Shusaku Imajo, Yasuhiro Nakazawa, and Satoshi Yamashita
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Fabrication ,Chemistry ,Analytical chemistry ,chemistry.chemical_element ,02 engineering and technology ,Calorimetry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Heat capacity ,Ruthenium oxide ,Magnetic field ,Metal ,visual_art ,0103 physical sciences ,Organic superconductor ,visual_art.visual_art_medium ,Physical and Theoretical Chemistry ,010306 general physics ,0210 nano-technology ,Indium - Abstract
We report design and constructional details of a small-sized sample stage for relaxation calorimetry by utilizing commercially available ruthenium oxide chip sensors. The reduction in addenda heat capacity attained by fabrication of chip sensors made it possible to measure absolute values of the heat capacity of molecular compounds weighing in an order of 101–2 μg with better temperature resolution. The result of calibration of the system by measuring 54.0 μg metal indium which shows superconductive transition at 3.2 K is presented in the former part. Upon determining thermodynamic parameters of γ and β corresponding to the electronic heat capacity coefficient and the lattice heat capacity coefficient, respectively, we confirm that accurate measurements by such small amount of sample are possible. The magnitude of heat capacity jump is also discussed by comparing 0 T data and those under magnetic fields. Using this new calorimetry system, we then measured heat capacity of κ-type organic superconductive salts of κ-(BEDT-TTF)2Cu(NCS)2 and κ-(BEDT-TTF)2Cu[N(CN)2]Br down to 0.7 K and discuss the nodal feature of the superconductive gap in them in the latter part. Measurements down to 3He temperature region with external magnetic fields will be possible for various organic conducting systems by a single piece of a crystal.
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- 2015
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25. Cooling-rate-controlled heat capacity measurements of organic superconductor (TMTSF)2ClO4
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Ryo Yoshimoto, Yasuhiro Nakazawa, Satoshi Morishita, Shuhei Fukuoka, Hiroki Akutsu, and Satoshi Yamashita
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Condensed matter physics ,Chemistry ,Slow cooling ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Heat capacity ,Ion ,Crystal ,Cooling rate ,0103 physical sciences ,Thermal ,Organic superconductor ,Physical and Theoretical Chemistry ,Anomaly (physics) ,010306 general physics ,0210 nano-technology - Abstract
An experimental technique for controlling cooling rate at low-temperature region in the heat capacity measurements was developed, and results of the heat capacity measurements of organic superconductor (TMTSF)2ClO4 cooled down with various cooling rates are presented. We succeeded in obtaining heat capacity data for a single piece of a crystal down to 0.7 K to study electronic states attained with slow cooling rates to extremely high cooling rate up to 500 K min−1. In the case of slow cooling at 0.17 K min−1, we observed a distinct peak of the superconductive transition which is almost consistent with previous results. The fraction of superconductive part is reduced in faster cooling rates, and no distinct peak structure in C p T −1 versus T 2 plot is observed around T c in the data of higher rate than 1.3 K min−1. In the rapid cooling region of 200 K min−1, clear reduction in electron density of states reflected in the change of the normal state γ value in the electronic heat capacity was observed. The sample shows an insulating character with a charge gap in the case of rapid cooling of 500 K min−1. We also discuss the feature of thermal anomaly related to the anion ordering around 24 K. A kind of glass-like freezing in residual conformational dynamics is suggested from the step-like decrease in C p T −1 around 19 K.
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- 2015
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26. Charge and Lattice Fluctuations in Molecule-Based Spin Liquids
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Taro Moriwaki, Yuka Ikemoto, Toshio Naito, Reizo Kato, Takashi Fujimoto, Masafumi Tamura, Kyuya Yakushi, Yasuhiro Nakazawa, and Takashi Yamamoto
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Physics ,Multidisciplinary ,Condensed matter physics ,media_common.quotation_subject ,Geometrical frustration ,lcsh:R ,lcsh:Medicine ,Frustration ,Infrared spectroscopy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Article ,Lattice (order) ,0103 physical sciences ,Antiferromagnetism ,Molecule ,lcsh:Q ,Condensed Matter::Strongly Correlated Electrons ,Quantum spin liquid ,lcsh:Science ,010306 general physics ,0210 nano-technology ,media_common - 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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- 2017
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27. Thermodynamics of the quantum spin liquid state of the single-component dimer Mott system κ−H3(Cat−EDT−TTF)2
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Yasuhiro Nakazawa, Satoshi Yamashita, Akira Ueda, and Hatsumi Mori
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Physics ,Spins ,Condensed matter physics ,Dimer ,02 engineering and technology ,Crystal structure ,021001 nanoscience & nanotechnology ,01 natural sciences ,Heat capacity ,chemistry.chemical_compound ,Deuterium ,chemistry ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,Quantum spin liquid ,010306 general physics ,0210 nano-technology ,Ground state ,Wilson ratio - Abstract
Thermodynamic properties of the proton-mediated single component dimer-Mott insulator of $\ensuremath{\kappa}\text{\ensuremath{-}}{\mathrm{H}}_{3}{(\mathrm{Cat}\text{\ensuremath{-}}\mathrm{EDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}$, which has a two-dimensional triangle lattice structure of $S=1/2$ spins, are reported. The extraordinary large electronic heat capacity coefficient $\ensuremath{\gamma}\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}58.8\phantom{\rule{0.28em}{0ex}}\mathrm{mJ}\phantom{\rule{0.16em}{0ex}}{\mathrm{K}}^{\ensuremath{-}2}\phantom{\rule{0.16em}{0ex}}\mathrm{mo}{\mathrm{l}}^{\ensuremath{-}1}$ observed by the low-temperature heat capacity measurements up to 6 T suggests the formation of the gapless spin liquid ground state. Although the magnetic interaction $J/{k}_{\mathrm{B}}$ is quite different from those of other dimer-Mott spin liquids, the thermodynamic feature scales well with the Wilson ratio of 1.4\char21{}1.6. The heat capacity measurements also detected that the deuteration of the proton-linkage changes the ground state to the nonmagnetic one with almost vanishing \ensuremath{\gamma}. Using the data of the deuterated compound, the accurate temperature dependence of the magnetic heat capacity reflecting on the low-energy excitations from the gapless spin liquids ground state is discussed.
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- 2017
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28. Ambient-pressure molecular superconductor with a superlattice containing layers of tris(oxalato)rhodate enantiomers and 18-crown-6
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Hiroki Akutsu, Alexander L. Morritt, Jordan R. Lopez, Yoshihiko Ihara, Lee Martin, Shusaku Imajo, and Yasuhiro Nakazawa
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Tris ,Superconductivity ,Condensed matter physics ,Superlattice ,18-Crown-6 ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Magnetic susceptibility ,0104 chemical sciences ,Ion ,Inorganic Chemistry ,chemistry.chemical_compound ,Crystallography ,chemistry ,Physical and Theoretical Chemistry ,0210 nano-technology ,Hybrid material ,Ambient pressure - Abstract
We report a novel multilayered organic–inorganic hybrid material, β″-(BEDT-TTF)2[(H2O)(NH4)2Rh(C2O4)3]·18-crown-6. This is the first molecular superconductor to have a superlattice with layers of both BEDT-TTF and 18-crown-6 and also the first with the anion tris(oxalato)rhodate. This is the 2D superconductor with the widest gap between conducting layers, where only a single donor packing motif is observed (β″). The strong 2D nature of this system strongly suggests that the superconducting transition is a Kosterlitz–Thouless transition. A superconducting Tc of 2.7 K at ambient pressure was found by transport measurements and 2.5 K by magnetic susceptibility measurements.
- Published
- 2017
29. Coupling of charge and lattice degrees of freedoms in θ-type BEDT-TTF compound probed by low-temperature heat capacity measurements
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Yoshiharu Takane, Yasuhiro Nakazawa, Satoshi Yamashita, Kosei Hino, and Ryo Yoshimoto
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Materials science ,Condensed matter physics ,Phonon ,Slow cooling ,Crystal structure ,Condensed Matter Physics ,Heat capacity ,Electronic, Optical and Magnetic Materials ,Magnetic field ,Condensed Matter::Superconductivity ,Lattice (order) ,Cluster (physics) ,Condensed Matter::Strongly Correlated Electrons ,Electrical and Electronic Engineering ,Ground state - Abstract
Thermodynamic investigations by heat capacity measurements at low temperature between 700 mK and 60 K with magnetic fields up to 8 T for θ-(BEDT-TTF) 2 RbZn(SCN) 4 and θ-(BEDT-TTF) 2 CsZn(SCN) 4 , where BEDT-TTF is bisethylenedithiotetrathiafulvalene are performed. In θ-(BEDT-TTF) 2 RbZn(SCN) 4 , the inter-site Coulomb repulsion produces a charge ordered ground state in the case of slow cooling while a kind of charge cluster glass state appears in rapidly cooled case. The observed finite γ term of 14.8 mJK −2 mol −1 for the rapidly cooled sample demonstrates that the electron density of states remains as metal-like clusters which are localized in the short-range scale. We also discuss the enhancement of the lattice heat capacity and appearance of a kind of Boson peak structure in C p even in a regular crystal lattice in θ-(BEDT-TTF) 2 CsZn(SCN) 4. The low energy phonon modes produced by enhanced charge fluctuations due to the inter-site Coulomb repulsion are the main course of these unusual lattice properties. The features reported here suggest that the coupling of charge degrees of freedom with lattices is important for the systems which do not form rigid charge ordered structures.
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- 2014
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30. Phonon Glass Induced by Electron Correlation
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Tetsuya Nomoto, Satoshi Yamashita, Hiroki Akutsu, Alexander I. Krivchikov, and Yasuhiro Nakazawa
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Materials science ,Electronic correlation ,Condensed matter physics ,Phonon ,General Physics and Astronomy ,01 natural sciences ,010305 fluids & plasmas ,Organic semiconductor ,chemistry.chemical_compound ,Thermal conductivity ,chemistry ,0103 physical sciences ,010306 general physics ,Tetrathiafulvalene - Abstract
We report the glass-like thermal conductivity behavior of two charge-glass (CG) formers in θ-type organic semiconductors composed by bis(ethylenedithio)tetrathiafulvalene (abbreviated as BEDT-TTF) ...
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- 2019
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31. Gap Symmetry of the Organic Superconductor λ-(BETS)2GaCl4 Determined by Magnetic-Field-Angle-Resolved Heat Capacity
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Shusaku Imajo, Hiroki Akutsu, Satoshi Yamashita, Takuya Kobayashi, Yasuhiro Nakazawa, Atsushi Kawamoto, and Hiroya Kumagai
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Materials science ,Condensed matter physics ,0103 physical sciences ,Organic superconductor ,General Physics and Astronomy ,Polar coordinate system ,010306 general physics ,01 natural sciences ,Heat capacity ,Symmetry (physics) ,010305 fluids & plasmas ,Magnetic field - Abstract
Angle-resolved heat capacity (ARHC) measurements with multi-directional magnetic fields for an organic superconductor λ-(BETS)2GaCl4 are performed to investigate the out-of-plane (polar angle) and ...
- Published
- 2019
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32. Antiferromagnetic fluctuations and proton Schottky heat capacity in doped organic conductor κ-(BEDT-TTF)4Hg2.78Cl8
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Akihito Naito, Satoshi Yamashita, Ryo Yoshimoto, and Yasuhiro Nakazawa
- Subjects
Heat capacity ,Materials science ,Spins ,Proton ,Condensed matter physics ,Relaxation (NMR) ,Calorimetry ,Electron ,Condensed Matter Physics ,Spin fluctuations ,Proton relaxation ,Magnetic field ,Electronic, Optical and Magnetic Materials ,Condensed Matter::Superconductivity ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Electrical and Electronic Engineering ,Organic conductor - Abstract
Low temperature heat capacity measurements of hole-doped organic conducting compound of κ-(BEDT-TTF) 4 Hg 2.78 Cl 8 were performed by the ac calorimetry and the thermal relaxation technique. It was observed that low temperature electronic heat capacity at 0 T can be fitted by a kind of spin fluctuations model for two-dimensional (2D) itinerant electrons. The enhancement of electronic heat capacity is originated from these magnetic fluctuations occur at extremely low temperature region. We also observed that the low temperature heat capacity under magnetic fields show large additional contribution explained by the two-level Schottky model of protons located on the edge of BEDT-TTF molecules. The strong spin fluctuations peculiar for 2D electrons in this hole-doped organic compound influence the relaxation process of proton spins to get thermal equilibrium state. This is the first example among organic conducting systems where magnetic fluctuations of itinerant electrons affect on the relaxation of proton spins. Similar tendency was observed in another hole-doped system of κ-(BEDT-TTF) 4 Hg 2.89 Br 8 of which magnitude is reduced down to 20–25% of that of κ-(BEDT-TTF) 4 Hg 2.78 Cl 8 .
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- 2013
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33. Condensation Energy for a Two-Gap Superconducting State in Nanoparticles
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Hiroyuki Kawabe, Hidemi Nagao, Yasuhiro Nakazawa, and Sergei Kruchinin
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Superconductivity ,Superconducting coherence length ,Materials science ,Critical level ,Article Subject ,Condensed matter physics ,Condensed Matter::Superconductivity ,Nanoparticle ,Parity (physics) ,Scattering process ,Size dependence - Abstract
Recent technology and experiments have fabricated high-quality superconducting MgB2 nanoparticles. We investigate properties of two-gap superconductivity in nanosized systems by using a two-sublevel model. In the present work, we analyze the results obtained for superconducting granules in the case of multiband superconductivity. We discuss the finite size effect in multiband superconductors. A definition of the critical level spacing of two-gap superconductivity is also presented, and we discuss the condensation energy and the parity gap of two-gap superconductivity in relation to the size dependence of those properties with two bulk gaps and the effective pair scattering process between two sublevels.
- Published
- 2013
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34. Development of heat capacity measurement system for single crystals of molecule-based compounds
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Shuhei Fukuoka, Yuki Horie, Satoshi Yamashita, and Yasuhiro Nakazawa
- Subjects
Differential scanning calorimetry ,Chemistry ,System of measurement ,Thermometer ,Analytical chemistry ,Thermodynamics ,Dilution refrigerator ,Calorimetry ,Physical and Theoretical Chemistry ,Condensed Matter Physics ,Adiabatic process ,Heat capacity ,Strain gauge - Abstract
We report on construction of a new low temperature heat capacity measurement system. This system was designed for performing thermodynamic investigation by thermal relaxation technique for small amount of samples at extremely low temperature region between 70 mK and 10 K. Two different calorimetry cells for this system were designed. One is a usual-type calorimetry cell consisting of tiny chip-type thermometer and strain gauge heater. The size of the sample stage has been reduced for measuring small samples. The other is designed for performing heat capacity measurements under magnetic fields of which magnitude and direction are accurately controlled. The calorimetry cells with heat capacity measurement unit can be mounted on a handy top-loading type dilution refrigerator of which outer diameter including the adiabatic space is 27 mm. We discuss basic performance and specification of the constructed cells and low temperature heat capacity data of an organic charge transfer salt obtained by this system.
- Published
- 2013
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35. Magnetic transition in dimerized radical cation salt of (BPDT-TTF)2ICl2 studied by heat capacity measurements
- Author
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Satoshi Yamashita, Yasuhiro Nakazawa, Takashi Yamamoto, Hiromi Taniguchi, Guoyang Guan, and Shuhei Fukuoka
- Subjects
Condensed matter physics ,Spin states ,Chemistry ,Calorimetry ,Condensed Matter Physics ,Heat capacity ,Magnetic susceptibility ,Ion ,Crystallography ,Charge ordering ,Radical ion ,Condensed Matter::Strongly Correlated Electrons ,Singlet state ,Physics::Chemical Physics ,Physical and Theoretical Chemistry - Abstract
Thermodynamic investigation using the relaxation calorimetry technique and the microchip calorimetry technique is performed to clarify low-temperature behaviors of a radical cation salt consisting of a donor molecule of bispropylenedithiotetrathiafulvalene (BPDT-TTF) and a linear anion of \({{\text{ICl}}_{2}^{-}}\). This compound has a layered structure similar to numerous BEDT-TTF compounds. The donor molecules form a dimerized arrangement in the layer. Temperature dependence of heat capacity obtained by the relaxation technique shows a broad hump structure around 20–25 K corresponding to the temperature where the magnetic susceptibility shows a drastic decrease due to the formation of the singlet spin state. The microchip calorimetry technique detected a step-like anomaly around 23 K in the temperature dependence of CpT−1 of which entropy is evaluated as only few % of Rln2 corresponding to the full entropy of localized π-electrons located on each dimer unit. The negligibly small T-linear term in the low-temperature heat capacity and absence of magnetic fields dependence below 3.2 K predict opening of rigid gap structure in the spin excitations, which is consistent with a spin-singlet formation due to the formation of spin-Peierls type ordering or charge ordering state.
- Published
- 2013
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36. A strongly polarized organic conductor
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Hiroki Akutsu, Jun-ichi Yamada, Keita Ishihara, Yasuhiro Nakazawa, Scott S. Turner, and Shin'ichi Nakatsuji
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chemistry.chemical_classification ,Materials science ,Salt (chemistry) ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Ion ,Conductor ,Crystal ,Crystallography ,Dipole ,chemistry ,Group (periodic table) ,Moment (physics) ,General Materials Science ,Polar space ,0210 nano-technology - Abstract
The electrically conducting salt α-(BEDT-TTF)2(PO-CON(CH3)CH2SO3)·3H2O crystallized in the polar space group, Pna21. 2D conducting BEDT-TTF layers and anion layers alternate along the crystallographic c axis. In the crystal, permanent dipoles of all anions point along the c axis, providing a net crystal dipole moment.
- Published
- 2016
37. Magnetocaloric effect in $Mn_2-pyrazole-[Nb(CN)_8]$ molecular magnet by relaxation calorimetry
- Author
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M. Gajewski, Yuji Miyazaki, S. Yamashita, Yasuhiro Nakazawa, R. Pełka, Magdalena Fitta, Dawid Pinkowicz, and Barbara Sieklucka
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Phase transition ,Materials science ,Critical phenomena ,Transition temperature ,Field dependence ,Thermodynamics ,02 engineering and technology ,Calorimetry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Heat capacity ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Tetragonal crystal system ,Magnetic refrigeration ,0210 nano-technology - Abstract
Magnetocaloric effect in {[Mn(pyrazole) 4 ] 2 [Nb(CN) 8 ]·4 H 2 O} n molecular magnet is reported. It crystallizes in tetragonal I4 1 /a space group. The compound exhibits a phase transition to a long range magnetically ordered state at T N ≈ 22.8 K . Temperature dependences of the magnetic entropy change Δ S M as well as the adiabatic temperature change Δ T ad due to applied field change μ 0 Δ H in the range of 0.1–9 T have been inferred from the relaxation calorimetry measurements. A systematic approximate approach has been used to determine the lattice contribution to the heat capacity. The maximum value of Δ S M for μ 0 Δ H = 5 T is 6.83 J mol −1 K −1 (6.65 J kg −1 K −1 ) at 24.3 K. The corresponding maximum value of Δ T ad is 1.4 K at 23.8 K. The temperature dependence of the exponent n characterizing the field dependence of Δ S M has been estimated. It attains the value of 0.64 at the transition temperature, which is consistent with the 3D Heisenberg universality class. A hitherto unobserved two-peak structure has been revealed in the temperature dependence of Δ T ad .
- Published
- 2016
38. Thermodynamic Properties of κ-(BEDT-TTF)2X Salts: Electron Correlations and Superconductivity
- Author
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Satoshi Yamashita and Yasuhiro Nakazawa
- Subjects
Superconductivity ,heat capacity ,organic superconductors ,Electronic correlation ,Condensed matter physics ,Chemistry ,General Chemical Engineering ,Mott insulator ,electron correlation ,Condensed Matter Physics ,Heat capacity ,Inorganic Chemistry ,chemistry.chemical_compound ,Pairing ,Condensed Matter::Superconductivity ,lcsh:QD901-999 ,Antiferromagnetism ,General Materials Science ,Condensed Matter::Strongly Correlated Electrons ,lcsh:Crystallography ,Tetrathiafulvalene ,Phase diagram - Abstract
Heat capacity measurements of κ-(BEDT-TTF)2X (BEDT-TTF: Bis(ethylendithio) tetrathiafulvalene, X: counteranions) which are classified as two-dimensional (2D) dimer-Mott system are reported. At first, we explain structural and electronic features originated from rigid dimerization in donor arrangement in 2D layers. The antiferromagnetic Mott insulating phase located at low-pressure region in the phase diagram shows vanishing γ electronic heat capacity coefficient in the heat capacity, which claims opening of a charge-gap in this insulating state. Then, a systematic change of the γ around the Mott boundary region is reported in relation to the glass freezing of ethylene dynamics. The thermodynamic parameters determined by ∆Cp/γTc of 10 K class superconductors, κ-(BEDT-TTF)2Cu(NCS)2 and κ-(BEDT-TTF)2Cu[N(CN)2]Br demonstrate that a rather large gap with a strong coupling character appears around the Fermi-surface. On the other hand, the low temperature heat capacity clearly shows a picture of nodal-gap structure due to an anisotropic pairing. The comparison with lower Tc compounds in the κ-type structure is also performed so as to discuss overall features of the κ-type superconductors. The heat capacity measurements of hole-doped systems containing mercury in the counteranions show an anomalous enhancement of γ, which is consistent with the T1−1 of NMR experiments etc. The results of heat capacity measurements under high pressures are also reported.
- Published
- 2012
39. Rich variety in the ground states of [Pd(dmit)2 ]2 salts, and the methodology for analysing intra-dimer interactions, inter-dimer interactions and MO levels
- Author
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Masafumi Tamura, Kyuya Yakushi, Reizo Kato, Yasuhiro Nakazawa, and Takashi Yamamoto
- Subjects
chemistry.chemical_compound ,Crystallography ,Computational chemistry ,Chemistry ,Dimer ,Hexagonal lattice ,Molecular orbital ,Condensed Matter Physics ,Electron spectroscopy ,Molecular electronic transition ,Electronic, Optical and Magnetic Materials ,Vibrational spectra - Abstract
A group of [Pd(dmit)2]2 salts, whose two-dimensional structures take (pesudo-) triangular lattice, has a diversity in the ground states. In order to investigate the ground states, we have developed the methodology for analysing subtle changes in the inter-molecular interactions and MO level using the vibrational and electronic spectroscopy. This methodology is applied to several [Pd(dmit)2]2 salts. We have found some relationships between the ground states and the inter-dimer and intra-dimer interactions under HOMO–LUMO inversion.
- Published
- 2012
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40. Microchip-calorimetry of organic charge transfer complex which shows superconductivity at low temperatures
- Author
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Yuki Muraoka, Satoshi Yamashita, Yasuhiro Nakazawa, and Takashi Yamamoto
- Subjects
Cryostat ,Superconductivity ,Chemistry ,Relaxation (NMR) ,Analytical chemistry ,Calorimetry ,Condensed Matter Physics ,Charge-transfer complex ,Calorimeter ,chemistry.chemical_compound ,Condensed Matter::Superconductivity ,Organic superconductor ,Condensed Matter::Strongly Correlated Electrons ,Physical and Theoretical Chemistry ,Instrumentation ,Tetrathiafulvalene - Abstract
We carried out thermodynamic measurements of organic charge transfer complex of κ-(BEDT-TTF) 2 Cu[N(CN) 2 ]Br, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene by TCG3880 chip device in order to examine capability of the chip calorimeter at low temperature region and under magnetic fields. TCG3880 chip is mounted on a 3 He cryostat available in combination with a superconductive magnet up to 7 T. Thermal anomalies related to the glass-like freezing of ethylene groups of BEDT-TTF molecules and the superconductive transition were observed. A frequency dependence of the thermal anomaly of the glass formation and a magnetic fields dependence of the thermal anomaly of the superconductive transition are reported. The results presented in this work demonstrate that the TCG3880 is quite useful for thermodynamic investigations of the organic charge transfer complex with much reduced sample quantity as compared with those of relaxation and adiabatic calorimetry.
- Published
- 2012
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41. Superconducting Phase Diagram of the Organic Superconductor κ-(BEDT-TTF)2Cu[N(CN)2]Br above 30 T
- Author
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Shusaku Imajo, Koichi Kindo, and Yasuhiro Nakazawa
- Subjects
Superconductivity ,Materials science ,Condensed matter physics ,0103 physical sciences ,Organic superconductor ,General Physics and Astronomy ,010306 general physics ,01 natural sciences ,010305 fluids & plasmas ,Phase diagram - Abstract
We examine high-magnetic-field features of the superconducting state of the organic superconductor, κ-(BEDT-TTF)2Cu[N(CN)2]Br, with an emphasis on the emergence of the Fulde–Ferrell–Larkin–Ovchinni...
- Published
- 2018
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42. Air-stable and high-mobility organic thin-film transistors of poly(2,5-bis(2-thienyl)-3,6-dihexadecyltheino[3,2-b]thiophene) on low-surface-energy self-assembled monolayers
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Mayumi Uno, Yasuhiro Nakazawa, Takeshi Nishikawa, Kengo Nakayama, and Jun Takeya
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Organic electronics ,Electron mobility ,Chemistry ,Self-assembled monolayer ,General Chemistry ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Biomaterials ,Organic semiconductor ,chemistry.chemical_compound ,Chemical engineering ,Thin-film transistor ,Triethoxysilane ,Materials Chemistry ,Thiophene ,Electrical and Electronic Engineering ,Thin film - Abstract
Air-stable and high-mobility polymer-based organic thin-film transistors are developed by employing low-surface-energy self-assembled monolayers and prolonged post-annealing. Carrier mobility in spin-coated thin films of a high-ionic-potential polymer semiconductor poly(2,5-bis(2-thienyl)-3,6-dihexadecyltheino[3,2-b]thiophene) reaches (0.08–0.17 cm2/V s with decyltriethoxysilane monolayers and 0.4–0.8 cm2/V s with (heptadecafluoro-1,1,2,2-tetrahydrodecyl)triethoxysilane monolayers. The values become higher with longer annealing above the glass-transition temperature. The mobility, threshold voltage and on–off ratio are stable in humid air during the whole period of the experiment for more than 2 weeks. The high-performance and the air-stability demonstrated in the polymer thin-film transistors have enhanced their applicability in large-area, low-cost and flexible electronic devices.
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- 2010
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43. Experimental and theoretical aspects of thermodynamic properties of quasi-1D and quasi-2D organic conductors and superconductors
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Sergei Kruchinin and Yasuhiro Nakazawa
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Superconductivity ,Materials science ,Condensed matter physics ,Specific heat ,Statistical and Nonlinear Physics ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Heat capacity ,Organic molecules ,0103 physical sciences ,010306 general physics ,0210 nano-technology ,Electrical conductor ,Electronic properties - Abstract
We deal with thermodynamic features of organic conductors and superconductors where itinerant [Formula: see text]-electrons/holes released from organic molecules are playing essential roles for electronic properties. Since they are low-dimensional electronic systems with relatively soft lattice framework, they show variety of phenomena related to electron correlations and electron–lattice coupling. The drastic changes of conductive and magnetic properties owing to quantum features of [Formula: see text]-electrons can be induced by external perturbations such as magnetic/electric field, pressure, etc. It is especially emphasized that the possible mechanism and relation with other phenomena of the superconductivity in [Formula: see text]-electrons system remains to be one of the interesting research areas in fundamental condensed matter science. In this review paper, we consider several topics of organic conductors and superconductors from the standpoints of thermodynamic experiments, data analyses and theories performed up to now. Starting from the overall picture of the electronic states in charge transfer complexes, thermodynamic properties of the quasi-one-dimensional systems, quasi-two-dimensional systems and [Formula: see text]–d interacting systems are reviewed. The thermodynamic parameters of the superconductive compounds in them are compared and discussed. The relations with crystal structures, electronic states, phase diagram and other experiments are also discussed in comparison with these thermodynamic properties. The possible pairing symmetries in organic superconductors and some models are mentioned in the last part. This review deals with a wide scope of theoretical and experimental topics in superconductivity in molecule-based conductive systems.
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- 2018
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44. Thermodynamic investigation by heat capacity measurements of κ-type dimer-Mott organic compounds with chemical pressure tuning
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Shinsuke Yamashita, Yasuhiro Nakazawa, Y. Matsumura, Shusaku Imajo, and Hiroki Akutsu
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Materials science ,Dimer ,Thermodynamics ,Boundary (topology) ,Statistical and Nonlinear Physics ,02 engineering and technology ,Type (model theory) ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Heat capacity ,chemistry.chemical_compound ,chemistry ,0103 physical sciences ,Pressure tuning ,010306 general physics ,0210 nano-technology ,Tetrathiafulvalene - Abstract
Thermodynamic discussion on the physical properties around the Mott boundary of the dimer-Mott system of [Formula: see text]-type (BEDT-TTF)2X system, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene and X denotes monovalent counter anions is performed by heat capacity measurements of the [Formula: see text]-(d[n,n] BEDT-TTF)2Cu[N(CN)2]Br of which donor molecules are partially deuterated. We compare temperature dependences of heat capacity of d[2,2], d[3,3] and d[4,4] compounds (defined as shown in Fig. 1) obtained in rapidly cooled and slowly cooled conditions. While the heat capacity of d[2,2] compound shows cooling rate dependence with the slight change of the absolute values Cp between 25 K and 50 K, the temperature dependences of the other compounds do not give drastic change by changing the cooling rate. The compounds of d[2,2] and d[3,3] located very close to the Mott boundary show peculiar hump structure in the C[Formula: see text]T[Formula: see text] that is related to the existence of a kind of lattice instability region around the first-order phase boundary. The temperature and chemical pressure dependences of the anomalous region are discussed in terms of the phase diagram in which the Mott boundary has peculiar rounding at low-temperature region.
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- 2018
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45. Development of light irradiation calorimetry system for molecule-based compounds
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Shusaku Imajo, Hiroki Akutsu, S. Kataoka, Yasuhiro Nakazawa, Y. Matsumura, and Shinsuke Yamashita
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Materials science ,Physics::Instrumentation and Detectors ,Light irradiation ,Statistical and Nonlinear Physics ,02 engineering and technology ,Calorimetry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Photochemistry ,01 natural sciences ,0103 physical sciences ,Molecule ,Development (differential geometry) ,010306 general physics ,0210 nano-technology - Abstract
Construction of a calorimetry system, by which the light irradiation to the surface area of molecular crystals at extremely low temperatures can be possible is reported. The development was performed based on the relaxation calorimetry technique to evaluate electronic structure using small amount of samples of molecular compounds where the electron correlation effects and electron–lattice coupling effects induce drastic change of the ground state. Detection of electronic structure changes occur as the light-induced phenomena becomes possible by this type of calorimetry apparatus. We report on the detailed structure of the small-sized calorimetry cells constructed for this purpose as well as the design of the calorimeter. The experimental results using organic superconductor and magnetic materials are given, which substantiate that the absolute value measurements under light irradiation are promising using the developed systems. Further possibility is also discussed.
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- 2018
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46. Heat capacity measurements of chiral and racemic molecular magnets
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Satoshi Yamashita, Shuhei Fukuoka, Katsuya Inoue, Hiroyuki Higashikawa, Yasuhiro Nakazawa, and Takashi Yamamoto
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Materials science ,Condensed matter physics ,Transition temperature ,Condensed Matter Physics ,Heat capacity ,Electronic, Optical and Magnetic Materials ,Magnetic field ,Magnetization ,Thermal ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Electrical and Electronic Engineering ,Anomaly (physics) ,Chirality (chemistry) - Abstract
Thermodynamic nature of the magnetic transitions of a cyano-bridged WV–CuII compound of [W(CN)8]4[Cu(pn)H2O]4[Cu(pn)]2·2.5H2O is studied by low-temperature heat capacity measurements. Distinct thermal anomalies were observed in the temperature dependence of the heat capacity at 7.8 K for chiral compound (S-enantiomer) and 7.2 K for racemic compound. They are associated with the antiferromagnetic transitions reported by the previous magnetization measurements. In the case of S-enantiomer, a shoulder structure of Cp/T has been observed just below the main peak of the antiferromagnetic transition temperature at 0 T. The shoulder grows to a sharp anomaly with a first order character by applying magnetic field of about 1 T in the b-axis direction. On the other hand, just a broadening of the peak was observed for racemic compound, which means that the complicated behavior under magnetic field is derived from the crystallographic chirality. We also studied the behavior of S-enantiomer with magnetic fields applied parallel to the c-axis and found that the first order transition is not induced. Appearance of the complicated peak structure including the first order character specific in the b-direction is ascribed to peculiar magnetic ordering derived from crystallographic chirality related to the Dzyaloshinskii–Moriya (DM) interaction.
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- 2010
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47. Low-temperature heat capacity measurements of κ-type organic superconductors under pressure
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Shuhei Fukuoka, Yasuhiro Nakazawa, N. Tokoro, and Osamu Kubota
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Superconductivity ,Materials science ,Condensed matter physics ,Organic superconductor ,Electrical and Electronic Engineering ,Condensed Matter Physics ,Adiabatic process ,Single crystal ,Heat capacity ,Ruthenium oxide ,Electronic, Optical and Magnetic Materials ,Ambient pressure ,Phase diagram - Abstract
Thermodynamic measurements using single crystals of κ-type organic superconductors have been performed under pressure and with magnetic field. We have adopted the ac temperature modulation technique for detecting relative variation of heat capacity as a function of temperature, since usual adiabatic condition inevitable for getting absolute values of heat capacities is difficult to attain under pressure. We used small ruthenium oxide chips as a heater and a thermometer and adhered them on the both side of single crystal and put them inside the Cu–Be cramp type pressure cell. The broad hump structure around 9 K which may be attributable to the thermal anomaly related to the superconductive transition was observed in κ-(BEDT-TTF) 2 Cu(NCS) 2 . However, the worse sensitivity of ruthenium oxide sensor (100 Ω at room temperature) in this temperature region make it difficult to separate the peak from the large background contribution. In the case of κ-[(BEDT-TTF) 0.9 (BEDSe-TTF) 0.1 ] 2 Cu[N(CN) 2 ]Br, we have observed a sharp peak in the heat capacity at ambient pressure and its downward shift at 3 kbar. The application of magnetic fields in the parallel direction to the superconductive layers was found to suppress the peak structure. The behaviors are consistent with the typical nature of 2D superconductors and the electronic phase diagram of κ-type organic salts.
- Published
- 2010
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48. Low temperature heat capacity measurements of the spin-liquid states of hydrogenated and deuterated κ-(BEDT-TTF)2Cu2(CN)3
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Satoshi Yamashita, T. Yamamoto, and Yasuhiro Nakazawa
- Subjects
Materials science ,Condensed matter physics ,Hydrogen ,Thermodynamics ,chemistry.chemical_element ,Electronic structure ,Condensed Matter Physics ,Heat capacity ,Electronic, Optical and Magnetic Materials ,Deuterium ,chemistry ,Molecule ,Condensed Matter::Strongly Correlated Electrons ,Hexagonal lattice ,Electrical and Electronic Engineering ,Quantum spin liquid ,Phase diagram - Abstract
Heat capacity measurements of organic triangular lattice compound κ-(BEDT-TTF) 2 Cu 2 (CN) 3 were performed to discuss the low energy excitations from the spin-liquid ground states. Existence of the T -linear electronic coefficient with finite electronic heat capacity coefficient γ was confirmed in three different samples from different batches, although small sample dependence was observed in the absolute values of the heat capacities. Concerning the sample in which hydrogen atoms in ethylene group in BEDT-TTF molecule have been substituted by deuterons, we have observed almost similar thermodynamic behavior as the hydrogenated sample. The absence of drastic change of electronic properties of this compound is consistent with the electronic phase diagram given by Kurosaki et al. [11] (Phys. Rev. Lett. 95 (2005) 17001). The obtained data are well consistent with the previous heat capacity experiments. The existence of the γ term demonstrates that the excitations from the quantum spin-liquid states show a gapless behavior at least down to 0.7 K.
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- 2010
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49. Low-temperature heat capacity of heptacopper(II) complex [Cu7(μ3-Cl)2(μ3-OH)6-(d-pen-disulfide)3]
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Takumi Konno, Satoshi Yamashita, Asako Igashira-Kamiyama, N. Tokoro, Junji Fujioka, and Yasuhiro Nakazawa
- Subjects
Zeeman effect ,Chemistry ,Stereochemistry ,Analytical chemistry ,Calorimetry ,Condensed Matter Physics ,Magnetic susceptibility ,Heat capacity ,symbols.namesake ,Excited state ,symbols ,Physical and Theoretical Chemistry ,Ground state ,Schottky anomaly ,Single crystal - Abstract
A single crystal calorimetry of a heptacopper(II) complex of [Cu7(μ3-Cl)2(μ3-OH)6-(d-pen-disulfide)3] which has a double-cubane structure supported by d-penicillaminedisulfides has been performed at low-temperature region below 8 K. This compound is a metal complex which contains seven Cu(II)s in a cluster unit. These Cu(II)s are magnetically coupled each other by strong intra-complex interactions. The heat capacities under magnetic fields exhibit Schottky type anomalies explained by the Zeeman splitting of the doublet ground state of the complex. The g-value of the ground state is evaluated as 1.86 from the systematic analysis of the Schottky peak under magnetic fields. The first excited state of the cluster seems to be separated at least by several Kelvins, which is consistent with the theoretical calculations and magnetic susceptibility results.
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- 2009
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50. Heat capacities of antiferromagnetic dimer-Mott insulators in organic charge-transfer complexes
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Yasuhiro Nakazawa and Satoshi Yamashita
- Subjects
Condensed matter physics ,Spins ,Chemistry ,Heisenberg model ,Mott insulator ,Electron ,Condensed Matter Physics ,Heat capacity ,Condensed Matter::Superconductivity ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Physical and Theoretical Chemistry ,Spin (physics) ,Single crystal - Abstract
Heat capacity measurements of quasi-two-dimensional Mott insulating compounds consisting of BEDT-TTF (bisethylendithiotetrathiafulubalene) donor molecules and counter anions were performed by the thermal relaxation calorimetry technique for single crystal samples. No distinct thermal anomalies at the predicted antiferromagnetic transition temperatures in κ-(BEDT-TTF)2Cu[N(CN)2]Cl (T N = 27 K) and β′-(BEDT-TTF)2ICl2 (T N = 22 K) were observed. These results demonstrate that the Mott insulating state of the organic salts which are dominated by the strong two-dimensional intra-layer antiferromagnetic interactions between neighboring S = 1/2 spins shows somewhat different features from the simple quasi-two-dimensional Heisenberg model with S = 1/2. The strong quantum fluctuations produced by the electron correlations suppress the long-range character of the spin correlations, which seems to be an important aspect of this kind of Mott insulating materials.
- Published
- 2009
- Full Text
- View/download PDF
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