Charge transport in charge-ordered layered crystals θ- (BEDT-TTF )2 MZn (SCN )4 (M=Cs,Rb ): Effects of long-range Coulomb interaction and the Pauli exclusion principle

Yamaguchi Takahide, Motoi Kimata, Kaori Hazama, Taichi Terashima, Shinya Uji, Takako Konoike, Hiroshi M. Yamamoto

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Abstract

We have measured the current-voltage (I-V) characteristics, dielectric properties, and magnetoresistances of insulating layered organic crystals θ- (BEDT-TTF)2 MZn (SCN)4 (M=Cs,Rb), in which electron-electron Coulomb interactions are considered to induce charge ordering. The in-plane I-V characteristics follow the power law with a large exponent that exceeds 10 in the low-temperature limit. The nonlinear I-V characteristics are attributed to electric field induced unbinding of pairs of an electron and a hole that are thermally excited and attracted to each other due to two-dimensional long-range Coulomb interaction. The temperature and frequency dependences of the in-plane dielectric constant for M=Cs are explained by the polarization of the electron-hole bound pairs, consistently with the I-V characteristics. The large dielectric anisotropy (≈100 at 0.6 K) observed for M=Cs suggests two-dimensional long-range Coulomb interaction, which is also consistent with the explanation of the nonlinear I-V curves. The organic crystals have a large positive magnetoresistance ratio, e.g., ≈ 10000% for M=Cs in a magnetic field of 10 T at 0.1 K. The magnetoresistance is nearly independent of the magnetic field orientation despite the highly two-dimensional charge transport, indicating that it is electron-spin related. The magnetoresistance may be caused by magnetic field induced parallel alignment of spins of mobile and localized electrons, both in the highest occupied molecular orbital of a BEDT-TTF molecule, and by the resulting suppression of conduction due to the Pauli exclusion principle.

Original languageEnglish
Article number235110
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume81
Issue number23
DOIs
Publication statusPublished - 2010 Jun 11
Externally publishedYes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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