13C-NMR Study of Charge Ordering State in the Organic Conductor, α-(BEDT-TTF)2I3

The pattern of charge ordering of the quasi two-dimensional organic conductor, alpha-(BEDT-TTF)(2)I-3 [BEDT-TTF: bis(ethylenedithio)tetrathiafulevalene], provides important information about the usual transport properties of this salt. Experiments on this salt have yielded conflicting results. Especially, the results of nuclear magnetic resonance (NMR) measurement and X-ray Diffraction (XRD) study have suggested contradictory charge patterns. To clarify these discrepancies, we performed C-13-NMR measurements using a single side C-13 enriched molecule. Above the metal-insulator transition temperature, the spin susceptibility at the B site decreased and that at the C site increased with decreasing temperature. Below the metal-insulator (M-I) transition temperature, however, the angular dependence of the NMR shift suggested that the charge order pattern was a horizontal stripe, in which the A(A') and B Molecules are charge rich sites and the A'(A) and C molecules are charge poor.