Crystals 2012, 2(4), 1502-1513; doi:10.3390/cryst2041502
Article

Magnetism and Pressure-Induced Superconductivity of Checkerboard-Type Charge-Ordered Molecular Conductor β-(meso-DMBEDT-TTF)2X (X = PF6 and AsF6)

1 The Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277–8581, Japan 2 Department of Chemistry, Graduate School of Science, Kobe University, Kobe, Hyogo 657–8501, Japan 3 Research Center for Neutron Science and Technology, CROSS, Tokai–mura 319–1106, Japan 4 Condensed Matter Research Center and Photon Factory, Institute of Materials Structure Science, KEK, Tsukuba 305–0801, Japan 5 Department of Physics, Toho University, Chiba 274-8510, Japan
* Author to whom correspondence should be addressed.
Received: 12 September 2012; in revised form: 5 November 2012 / Accepted: 14 November 2012 / Published: 29 November 2012
(This article belongs to the Special Issue Molecular Conductors)
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Abstract: The metallic state of the molecular conductor β-(meso-DMBEDT-TTF)2X (DMBEDT-TTF = 2-(5,6-dihydro-1,3-dithiolo[4,5-b][1,4]dithiin-2-ylidene)-5,6-dihydro-5,6-dimethyl-1,3-dithiolo[4,5-b][1,4]dithiin, X = PF6, AsF6) is transformed into the checkerboard-type charge-ordered state at around 75–80 K with accompanying metal-insulator (MI) transition on the anisotropic triangular lattice. With lowering temperatures, the magnetic susceptibility decreases gradually and reveals a sudden drop at the MI transition. By applying pressure, the charge-ordered state is suppressed and superconductivity appears in β-(meso-DMBEDT-TTF)2AsF6 as well as in the reported β-(meso-DMBEDT-TTF)2PF6. The charge-ordered spin-gapped state and the pressure-induced superconducting state are discussed through the paired-electron crystal (PEC) model, where the spin-bonded electron pairs stay and become mobile in the crystal, namely the valence-bond solid (VBS) and the resonant valence bonded (RVB) state in the quarter-filled band structure.
Keywords: superconductor; dimer state; checkerboard-type charge ordering; singlet state; valence bond solid; paired-electron crystal

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MDPI and ACS Style

Shikama, T.; Shimokawa, T.; Lee, S.; Isono, T.; Ueda, A.; Takahashi, K.; Nakao, A.; Kumai, R.; Nakao, H.; Kobayashi, K.; Murakami, Y.; Kimata, M.; Tajima, H.; Matsubayashi, K.; Uwatoko, Y.; Nishio, Y.; Kajita, K.; Mori, H. Magnetism and Pressure-Induced Superconductivity of Checkerboard-Type Charge-Ordered Molecular Conductor β-(meso-DMBEDT-TTF)2X (X = PF6 and AsF6). Crystals 2012, 2, 1502-1513.

AMA Style

Shikama T, Shimokawa T, Lee S, Isono T, Ueda A, Takahashi K, Nakao A, Kumai R, Nakao H, Kobayashi K, Murakami Y, Kimata M, Tajima H, Matsubayashi K, Uwatoko Y, Nishio Y, Kajita K, Mori H. Magnetism and Pressure-Induced Superconductivity of Checkerboard-Type Charge-Ordered Molecular Conductor β-(meso-DMBEDT-TTF)2X (X = PF6 and AsF6). Crystals. 2012; 2(4):1502-1513.

Chicago/Turabian Style

Shikama, Takahisa; Shimokawa, Tatsuya; Lee, Sanguchul; Isono, Takayuki; Ueda, Akira; Takahashi, Kazuyuki; Nakao, Akiko; Kumai, Reiji; Nakao, Hironori; Kobayashi, Kensuke; Murakami, Youichi; Kimata, Motoi; Tajima, Hiroyuki; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Nishio, Yutaka; Kajita, Koji; Mori, Hatsumi. 2012. "Magnetism and Pressure-Induced Superconductivity of Checkerboard-Type Charge-Ordered Molecular Conductor β-(meso-DMBEDT-TTF)2X (X = PF6 and AsF6)." Crystals 2, no. 4: 1502-1513.

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