Emergence of charge degrees of freedom under high pressure in the organic dimer-Mott insulator β′-(BEDT - TTF) 2 ICl 2

K. Hashimoto, R. Kobayashi, H. Okamura, H. Taniguchi, Y. Ikemoto, T. Moriwaki, S. Iguchi, Makoto Naka, S. Ishihara, T. Sasaki

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To elucidate the pressure evolution of the electronic structure in an antiferromagnetic dimer-Mott (DM) insulator β′-(BEDT-TTF)2ICl2, which exhibits superconductivity at 14.2 K under 8 GPa, we measured the polarized infrared (IR) optical spectra under high pressure. At ambient pressure, two characteristic bands due to intra- and interdimer charge transfers have been observed in the IR spectra, supporting that this salt is a typical half-filled DM insulator at ambient pressure. With increasing pressure, however, the intradimer charge transfer excitation shifts to much lower energies, indicating that the effective electronic state changes from half-filled to 3/4-filled as a result of weakening of dimerization. This implies that the system approaches a charge-ordered state under high pressure, in which charge degrees of freedom emerge as an important factor. The present results suggest that charge fluctuation inside of dimers plays an important role in the high-temperature superconductivity.

Original languageEnglish
Article number085149
JournalPhysical Review B - Condensed Matter and Materials Physics
Issue number8
Publication statusPublished - 2015 Aug 28
Externally publishedYes


ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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