C13NMR study on the charge-ordering saltα′−(BEDT-TTF)2IBr2

Shinji Hirose, Atsushi Kawamoto
2009 Physical Review B  
Among quasi-two-dimensional organic conductors, ͑BEDT-TTF͒ 2 X, what form the two column structure of ␣ or is thought to show a charge-ordering insulating state. The ␣Ј modification is the other candidate for a charge-ordering state. To determine the existence of a charge-ordering state and electron magnetism in the ␣Ј phase, which has a symmetry that differs from that of the ␣ and phases, we utilized 13 C-NMR to examine ␣Ј-͑BEDT-TTF͒ 2 IBr 2 in which one side of the central carbon on the
more » ... TF molecule is substituted with 13 C nuclei. We observed changes in its spectrum at 200 K. The angular dependence of the NMR shift at 15 K indicated that the charge-ordering pattern is intracolumn disproportionation and the ratio of charge disproportionation on the spin-poor site and spin-rich sites is almost 1:0. The angle dependence of NMR spectrum at 60 K suggests that the hyperfine coupling tensor in the paramagnetic charge-ordering state is determined not only by the charge density of on-site molecules but also by the contribution of off-site molecules. The change in hyperfine coupling tensor must be taken into account in NMR studies of the paramagnetic CO state.
doi:10.1103/physrevb.80.165103 fatcat:ffjy3xewwzfh5bnmavrznmxhgy