J. Phys. IV France
Volume 131, December 2005
Page(s) 3 - 8
Published online 18 January 2006
International Workshop on Electronic Crystals
S. Brazovskii, P. Monceau and N. Kirova
J. Phys. IV France 131 (2005) 3-8

DOI: 10.1051/jp4:2005131002

Charge disproportionation, everywhere!

T. Takahashi1, K. Hiraki1, S. Moroto1, N. Tajima2, Y. Takano1, Y. Kubo1, H. Satsukawa1, R. Chiba1, H.M. Yamamoto2, R. Kato2 and T. Naito3

1  Department of Physics, Gakushuin University, Tokyo 171-8588, Japan
2  RIKEN, The Institute of Physical and Chemical Research (RIKEN), JST-CREST, Saitama 351-0198, Japan
3  Creative Research Initiative "Sosei" Hokkaido University, Hokkaido 001-0020, Japan

Charge disproportionation (CD) recently observed in many organic conductors is reviewed. CD is closely related to the charge ordering (CO) but is observed even when no long range CO is established. In a $\theta
$-phase BEDT-TTF salt, (BEDT-TTF)2RbZn(SCN)4, an extremely slow dynamics of CD has been observed above $T_{\rm MI}$. A similar phenomenon is also observed in the Cs-analog, (BEDT-TTF)2CsZn(SCN)4. However, a spin-singlet ground state without CD is suggested in this salt at low temperatures. It is shown that $\alpha $-(BETS)2I3 exhibits CD at low temperatures, as in $\alpha $-(BET-TTF)2I3. Recently, an abnormal line broadening has been observed in 13C-NMR of (TMTSF)2FSO3 under pressure as well as in 77Se-NMR of $\lambda$-(BETS)2FeCl4 in a high field. We expect that both are very likely caused by a large CD among the organic molecular sites.

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