Spectroscopic studies of charge‐ordering system in organic conductors

Charge localization generates a non‐uniform charge distribution in some organic conductors. Phase transitions accompanying such a localization of charge are studied by using infrared and Raman spectroscopy. We first introduce θ‐(BEDT‐TTF) 2 MM′(SCN) 4 (M=Rb, Cs, Tl; M′=Zn, Co) as typical examples of a charge‐ordering system, where BEDT‐TTF is bis(ethylenedithio)tetrathiafulvalene. We apply the same spectroscopic technique to α′‐(BEDT‐TTF) 2 IBr 2 , θ‐(BDT‐TTF) 2 Cu(NCS) 2 , and (TTM‐TTP)I 3 , which show the phase transitions from low‐resistivity to high‐resistivity state, where TTM‐TTP is 2,5‐bis[4,5‐bis(methylsulfonyl)‐1,3‐dithiol‐2‐ylidene]‐1,3,4,6‐tetrathiapentalene.