Investigations on Electronic States of Molecule-based Compounds by High-Pressure AC Calorimetry

Nakazawa, Yasuhiro; Yoshimoto, Ryo; Fukuoka, Shin-Ichi

doi:10.2174/1877944104666140825204911

Cited by 4 publications

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“…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%

“…However, those with lower T c compounds tend to have larger γ* values despite the heat capacity giving a distinct peak at the transition. In the cases of κ-(BEDT-TTF) 2 Ag(CN) 2 H 2 O and κ-(MDT-TTF) 2 AuI 2 , the reported γ* values are 5.1 mJK −2 mol −1 and 5.9 mJK −2 mol −1 , respectively [33,49]. A more recent experiment on κ-(BEDT-TTF) 2 Ag(CN) 2 H 2 O claims a smaller γ* value (less than 2 mJK −2 mol −1 ) using the fitting of the d-wave model [60].…”

Section: Normal State Electronic Heat Capacity Coefficient γ and The mentioning

confidence: 98%

“…Measurements are available over a wide temperature range from a low temperature of about 0.7 K up to about 20 K while reducing the sample amount to 200 µg-2 mg [41][42][43][44][45]. The construction details are reported elsewhere [33,41,42]. The adoption of extremely small chips as the thermometer and the accurate detection using the four-terminal method have worked well to achieve high-resolution detection for organic superconductors, providing heat capacity measurements in the low-temperature region.…”

Section: Calorimetry Apparatus To Measure the Heat Capacity Under Prementioning

confidence: 99%

“…(The data are from Ref. [33].) The dashed curves in the figure are a guide for the eyes to see temperature dependencies.…”

Section: Chemical Pressure Effect On Dimer-mott Organic Compoundsmentioning

confidence: 99%

“…The change in γ occurs in a region far away from the boundary, suggesting that the band-like feature reflecting in the electronic density of states systematically varies. In the discussion on this region, we include data of solid solution compounds of BEDT-TTF and BEDSe-TTF with X = Cu[N(CN) 2 ]Br since light doping (less than 10%) of BEDSe-TTF tends to reduce the T c by keeping the bulk superconductive feature [33]. The arrow on the left side of the figure clearly indicates that the γ values increase as the U/W ratio increases.…”

Section: Normal State Electronic Heat Capacity Coefficient γ and The mentioning

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: Chemical Pressure Effect On Dimer-mott Organic Compoundsmentioning

confidence: 63%

Section: Normal State Electronic Heat Capacity Coefficient γ and The mentioning

confidence: 98%

Section: Calorimetry Apparatus To Measure the Heat Capacity Under Prementioning

confidence: 99%

“…(The data are from Ref. [33].) The dashed curves in the figure are a guide for the eyes to see temperature dependencies.…”

Section: Chemical Pressure Effect On Dimer-mott Organic Compoundsmentioning

confidence: 99%

Section: Normal State Electronic Heat Capacity Coefficient γ and The mentioning

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

Muraoka

Imajo

Akutsu

et al. 2016

J Therm Anal Calorim

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Thermodynamic measurements of doped dimer-Mott organic superconductor under pressure

Matsumura

Akutsu

Nakazawa

2022

Low Temperature Physics

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Thermal anomalies in the temperature dependence of the heat capacity around the superconducting transition of a hole-doped superconductor, κ–(BEDT-TTF)4Hg2.89Br8, which is known as a dimer-Mott triangle lattice system are investigated by the ac modulation technique under external pressure. To detect the electronic phase transition under applied pressure conditions for a single crystal sample, we have improved resolution of the ac modulation technique. By tracking the appropriate frequency during the temperature scan measurement, we succeed in detecting the thermal anomaly with the applied pressure of 0.3 GPa where the electronic state is located in the crossover region of non-Fermi liquid to Fermi liquid. Application of the external magnetic fields of H = 2 and 6 T in the in-plane direction reveals that the superconductivity in this doped triangle lattice of molecular dimers is relatively stable against the magnetic field.

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Investigations on Electronic States of Molecule-based Compounds by High-Pressure AC Calorimetry

Cited by 4 publications

References 0 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

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

Thermodynamic measurements of doped dimer-Mott organic superconductor under pressure

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