J. Phys. IV France
Volume 114, April 2004
Page(s) 149 - 151

J. Phys. IV France
114 (2004) 149
DOI: 10.1051/jp4:2004114036

Dynamical fluctuation of the site-charge density in metallic ${\beta'' }$-(BEDT-TTF)(TCNQ)

Kyuya Yakushi1, 1, Mikio Uruichi1, Hiroshi Yamamoto2 and Reizo Kato2

1  Institute for Molecular Science, Nishigo-naka 38, Myodaiji, Okazaki 444-8585, Japan
2  RIKEN, JST-CREST, 2-1, Hirosawa, Wako-shi, Saitama 351-0198, Japan

We We present the temperature dependences of the reflectance and Raman spectra of metallic ${\beta'' }$-(BEDT-TTF)(TCNQ). BEDT-TTF and TCNQ form quasi-one-dimensional bands mainly extended along the a- and c-axes, respectively, and their interaction along the b-axis is weak. The degree of charge transfer from BEDT-TTF to TCNQ is about 0.5, so that each band forms a $\raise.5ex\hbox{$\scriptstyle 3$ }\kern-.1em/
\kern-.15em\lower.25ex\hbox{$\scriptstyle 3$ } $ - and $\raise.5ex\hbox{$\scriptstyle 1$ }\kern-.1em/
\kern-.15em\lower.25ex\hbox{$\scriptstyle 4$ } $ -filled band. With lowering temperature, the optical conductivity associated with BEDT-TTF band approaches a Drude-like shape without structural distortion. On the other hand, the optical conductivity of TCNQ band deviates from a Drude-like response with a 2k $_{\rm F}$ or 4k $_{\rm F}$ lattice distortion. At room temperature, the Raman-active $\nu _{2}$ and infrared-active $\nu _{27}$ modes of BEDT-TTF showed a splitting, that is, the charge on the BEDT-TTF chain is nearly localized. Interestingly, these split bands merged at around 100 K. The Raman-active $\nu _{4}$ of TCNQ keeps the frequency corresponding to TCNQ 0.5-. Therefore, the charge in TCNQ column is equally sheared by two or four TCNQ molecules. Key words. Organic conductors - charge ordering - infrared and Raman - BEDT-TTF.

© EDP Sciences 2004