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Crystals 2012, 2(3), 741-761; doi:10.3390/cryst2030741
Review

Thermodynamic Properties of κ-(BEDT-TTF)2X Salts: Electron Correlations and Superconductivity

1,*  and 2
Received: 11 April 2012; in revised form: 16 June 2012 / Accepted: 18 June 2012 / Published: 29 June 2012
(This article belongs to the Special Issue Molecular Conductors)
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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.
Keywords: heat capacity; electron correlation; Mott insulator; organic superconductors heat capacity; electron correlation; Mott insulator; organic superconductors
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Nakazawa, Y.; Yamashita, S. Thermodynamic Properties of κ-(BEDT-TTF)2X Salts: Electron Correlations and Superconductivity. Crystals 2012, 2, 741-761.

AMA Style

Nakazawa Y, Yamashita S. Thermodynamic Properties of κ-(BEDT-TTF)2X Salts: Electron Correlations and Superconductivity. Crystals. 2012; 2(3):741-761.

Chicago/Turabian Style

Nakazawa, Yasuhiro; Yamashita, Satoshi. 2012. "Thermodynamic Properties of κ-(BEDT-TTF)2X Salts: Electron Correlations and Superconductivity." Crystals 2, no. 3: 741-761.

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