Thermal anomaly around the superconductive transition of κ-(BEDT-TTF)2Cu(NCS)2 with external pressure and magnetic field control

Muraoka, Yoshiho; Imajo, Shusaku; Akutsu, Hiroki; Nakazawa, Yasuhiro

doi:10.1007/s10973-016-5246-8

Cited by 6 publications

(6 citation statements)

References 24 publications

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“…This anomaly is associated with the superconductive transition since the peak temperature and the peak shape resemble the preceding data obtained by the thermal relaxation technique in Figure 4c. Upon applying magnetic fields almost parallel to the plane in the present pressure calorimetry set up, the anomaly is suppressed through comparative analyses of the magnetic field dependence, as already reported [32]. The data obtained up to 7 T has a constant shift of C p T −1 values at different magnetic fields (Figure 5a).…”

Section: Heat Capacity Of κ-(Bedt-ttf)2x Under Pressuresupporting

confidence: 70%

“…This is typical for strong coupling systems, but 4-5 K class compounds have a smaller mean field type peak. The systematic change in the peak shape indicates a gradual crossover from a strong coupling region near the boundary to a weak coupling region in the superconductive phase, as shown schematically in Figure 8 (right) [32,33]. Although some exceptions exist, such as κ-(BEDT-TTF) 2 I 3 being reported to have strong coupling features [59], the overall tendency seems to be consistent with the external pressure controlled effects.…”

Section: Chemical Pressure Effect On Dimer-mott Organic Compoundsmentioning

confidence: 63%

“…To confirm the thermodynamic peak in the ac heat capacity data obtained by the high-pressure calorimetric system, we have analyzed the data at ambient pressure and compared them with the relaxation calorimetry data. Figure 5a shows the ac heat capacity measurement results at ambient pressure obtained using a high-pressure calorimeter as a C p T −1 vs. T 2 plot [32]. A thermal anomaly is detected as a hump structure around 9 K in this plot, although there is a rather large background due to the addenda heat capacity in the pressure cell.…”

Section: Heat Capacity Of κ-(Bedt-ttf)2x Under Pressurementioning

confidence: 97%

“…Figure 5a shows the ac heat capacity measurement results at ambient pressure obtained using a high-pressure calorimeter as a CpT −1 vs. T 2 plot [32]. A thermal anomaly is detected as a hump structure around 9 K in this plot, although there is a rather large background due to the addenda heat capacity in the pressure cell.…”

Section: Heat Capacity Of κ-(Bedt-ttf)2x Under Pressurementioning

confidence: 97%

“…Here, ΔCp is determined as the discrepancy of the heat capacity values in the 0-T and 7-T data assuming that the thermal anomaly due to superconductive transition is almost reduced in a magnetic field of 7 T. The analytic details were reported in Ref. [32]. The peak resembles the typical shape of the superconductive transition with a strong coupling feature.…”

Section: Heat Capacity Of κ-(Bedt-ttf)2x Under Pressurementioning

confidence: 99%

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Thermodynamic Picture of Dimer-Mott Organic Superconductors Revealed by Heat Capacity Measurements with External and Chemical Pressure Control

et al. 2018

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This article reviews and discusses the thermodynamic properties of dimer-Mott-type molecular superconductive compounds with (BEDT-TTF) 2 X composition, where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene and X denotes counter-anions, respectively. We focus mainly on the features occurring in the κ-type structure in which the d-wave superconductive phase appears depending on the Coulomb repulsion U and the bandwidth W, which is tunable by external and chemical pressures. First, we report the high-pressure ac (alternating current) calorimetry technique and experimental system constructed to measure single-crystal samples of molecule-based compounds to derive low-temperature thermodynamic parameters. Using extremely small resistance chips as a heater and a thermometer allows four-terminal detection of an accurate temperature and its oscillation in the sample part with sufficient sensitivity. From the analyses of the temperature dependence of the ac heat capacity of κ-(BEDT-TTF) 2 Cu(NCS) 2 under external pressures, we discuss the changes in the peak shape of the thermal anomaly at the superconductive transition temperature T c at various external pressures p. The rather sharp peak in C p T −1 at T c = 9.1 K with a strong coupling character at ambient pressure is gradually reduced to weaker coupling as the pressure increases to 0.45 GPa concomitant with suppression of the transition temperature. This feature is compared with the systematic argument of the chemical-pressure effect on the basis of thermal anomalies around the superconductive transition of κ-(BEDT-TTF) 2 X compounds and other previously studied typical dimer-Mott 2:1 compounds. Finally, the discussion is extended to the chemical pressure effect on the normal state electronic heat capacity coefficient γ obtained by applying magnetic fields higher than H c2 and the residual γ*, which remains in the superconductive state due to the induced electron density of states around the node structure. From the overall arguments with respect to both chemical and external pressures, we suggest that a crossover of the electronic state inside the superconductive phase occurs and the coupling strength of electron pairs varies from the electron correlation region near the metal-insulator boundary to the band picture region.

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Section: Heat Capacity Of κ-(Bedt-ttf)2x Under Pressuresupporting

confidence: 70%

Section: Chemical Pressure Effect On Dimer-mott Organic Compoundsmentioning

confidence: 63%

Section: Heat Capacity Of κ-(Bedt-ttf)2x Under Pressurementioning

confidence: 97%

Section: Heat Capacity Of κ-(Bedt-ttf)2x Under Pressurementioning

confidence: 97%

Section: Heat Capacity Of κ-(Bedt-ttf)2x Under Pressurementioning

confidence: 99%

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Thermodynamic Picture of Dimer-Mott Organic Superconductors Revealed by Heat Capacity Measurements with External and Chemical Pressure Control

et al. 2018

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Molecular conductors as nanoparticles in the presence of long-chain alkyl imidazolium salts or amphiphilic molecules

Foulal

Hajjaji

Trif

et al. 2016

J Therm Anal Calorim

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Nanoparticles of two molecule-based conductors namely, TTFTCNQ and TTF[Ni(dmit) 2 ] 2 , have been prepared in organic solution in the presence of ionic or non-ionic species bearing a long-chain alkyl group, acting as growth controlling agents. The size, morphology and state of dispersion of the nanoparticles depended on the nature of the growth-controlling agent and the reaction temperature. In the presence of a long-chain-alkyl-based ionic liquid at -50 °C, electron micrographs evidence that TTFTCNQ nano-objects are frequently elongated, whereas TTF[Ni(dmit) 2 ] 2 nanoparticles are aggregated. In the presence of a neutral long-chain-alkyl-based imine at room temperature, nanoparticles are spherical (mean diameter less than 20 nm) and well dispersed. Vibration spectra evidence that the amounts of charge transfer for TTFTCNQ and TTF[Ni(dmit) 2 ] 2 as nano-objects are very similar to those for the same phases as bulk materials. According to the thermoanalytical investigations, the prepared nanoparticles are stable thermally up to approximately 200 °C, their decomposition is generally a multi-step process. Their heat treatment results in various sulfur containing volatiles (CS 2 , SO 2 , H 2 S), moreover HCN is also detected in the case of nitrogen containing molecules (TCNQ).

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Construction of a thermal conductivity measurement system for small single crystals of organic conductors

Nomoto

Imajo

Akutsu

et al. 2018

J Therm Anal Calorim

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Thermal anomaly around the superconductive transition of κ-(BEDT-TTF)2Cu(NCS)2 with external pressure and magnetic field control

Cited by 6 publications

References 24 publications

Thermodynamic Picture of Dimer-Mott Organic Superconductors Revealed by Heat Capacity Measurements with External and Chemical Pressure Control

Thermodynamic Picture of Dimer-Mott Organic Superconductors Revealed by Heat Capacity Measurements with External and Chemical Pressure Control

Molecular conductors as nanoparticles in the presence of long-chain alkyl imidazolium salts or amphiphilic molecules

Construction of a thermal conductivity measurement system for small single crystals of organic conductors

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