open access

https://hdl.handle.net/2115/39842

C-13 NMR study on the charge-ordering salt α'-(BEDT-TTF)2IBr2

英語

superconducting transitions

2009-10

American Physical Society

Physical Review B

80(16)

165103

Among quasi-two-dimensional organic conductors, (BEDT-TTF)2X, what form the two column structure of α or θ is thought to show a charge-ordering insulating state. The α' modification is the other candidate for a charge-ordering state. To determine the existence of a charge-ordering state and electron magnetism in the α' phase, which has a symmetry that differs from that of the α and θ phases, we utilized C-13-NMR to examine α'-(BEDT-TTF)2IBr2 in which one side of the central carbon on the BEDT-TTF molecule is substituted with C-13 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.

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© 2009 The American Physical Society

1098-0121