Charge ordering in organic conductors

Present status of experiments on charge ordering (CO) phenomena observed in organic molecular conductors is reviewed. Experimental techniques to detect and analyze the CO, i.e., NMR, X-ray and Infrared/Raman spectroscopy, are described and the experimental results in typical materials exhibiting CO are summarized. (DI-DCNQI)(2)Ag, (TMTTF)(2)X, alpha-(BEDT-TTF)(2)I-3, theta-(BEDT-TTF)(2)RbZn(SCN)(4) and related materials are discussed. Charge disproportionation without long-range order observed in numbers of materials are also included.