J. Phys. Soc. Jpn. 88, 034705 (2019) [5 Pages]

Charge Order and Poor Glass-forming Ability of an Anisotropic Triangular-lattice System, θ-(BEDT-TTF)2TlCo(SCN)4, Investigated by NMR

+ Affiliations
1Department of Applied Physics, University of Tokyo, Bunkyo, Tokyo 113-8656, Japan2The Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba 277-8581, Japan

The family of layered organic conductors, θ-(BEDT-TTF)2MM′(SCN)4, are anisotropic triangular-lattice systems with quarter-filled bands and exhibit charge order instability or glassy charge freezing. We have investigated the compound with MM′ = TlCo, which was suggested to show a charge order by transport studies, through 13C NMR spectroscopy. The profiles of NMR spectra and the nuclear spin–lattice relaxation rate provide evidence for a charge order with a charge disproportionation ratio of \(7:1\) or larger. The nuclear spin–spin relaxation rate, 1/T2, keeps increasing as the charge-ordering temperature is approached from above, indicating an increase in the spectral weight of fluctuations on the order of kHz or their slowing down toward the kHz range. This behavior, however, differs from that of the charge order/glass systems, MM′ = RbZn, and CsZn salts, which show a peak in 1/T2 with decreasing temperature, signifying a slowing down of charge fluctuations to below the kHz range. The insufficient slowing down for MM′ = TlCo demonstrates the poor glass-forming ability suggested by a previous transport study from the viewpoint of the dynamics.

©2019 The Physical Society of Japan


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