Nonuniform site-charge distribution and fluctuations of charge order in the metallic state ofα−(BEDT-TTF)2I3

Abstract

We present the site-charge distribution in the charge-ordered and metallic states of ␣-͑BEDT-TTF͒ 2 I 3 , based on the assignment of the C v C stretching modes 2 , 3 , and 27 of ␣-͑BEDT-TTF͒ 2 I 3 with the aid of 13 C-and deuterium-substituted compounds. The nonuniform site charges in both the metallic and insulating phases were consistent with those determined by a recent x-ray diffraction study. Comparing the line shapes of the chargesensitive vibrational modes of ␣-͑BEDT-TTF͒ 2 I 3 with those of isostructural ␣-͑BEDT-TTF͒ 2 NH 4 Hg͑SCN͒ 4 , we propose a thermally activated fluctuation of charge order in the metallic phase of ␣-͑BEDT-TTF͒ 2 I 3. This fluctuation was considerably suppressed above 0.65 GPa. The optical conductivity in the metallic phase shows no Drude response.

Infrared and Raman Studies of Charge Ordering in Organic Conductors, BEDT-TTF Salts with Quarter-Filled Bands

“…Yue et al, showed that the linewidth of metallic α-I 3 is about two to three times as large as that of α-NH 4 Hg [130]. As shown in Figure 21a, the linewidth of ν 27 of α-I 3 is much broader than the charge-insensitive mode such as the CH 2 bending mode.…”

“…Recently, Alemany et al, pointed out that the hydrogen bond between the ethylene groups of BEDT-TTF and I 3 − plays an essential role in the CO transition of α-I 3 [129]. In the MI transition of α-I 3 , Raman [111] and infrared [130] spectra showed drastic changes as seen in Figure 18. The assignment of these bands along with vibronic bands was conducted with the aid of 13 C and deuterium substituted compounds.…”

“…Similar splitting of ν 27 is described in ref. [130]. The crystal of θ-I 3 belongs to the monoclinic system with space group of P2 1 /c, and the unit cell contains four BEDT-TTFs.…”

“…Based on the assignment, it becomes clear that the ν 2 and ν 27 modes are split into two groups, ν 2P and (ν 2R1 , ν 2R2 ) in the Raman spectrum and (ν 27P ) in the infrared spectrum as shown in Figure 18. Applying the linear relationship [46] to the ν 27 mode (50 K), the site charge distribution is estimated as (0.8, 0.7, 0.3, 0.2) [130], which are approximately equal to the values (0.85, 0.80, 0.20, 0.15) estimated by Ivek et al [133]. The CO amplitude (Δρ max = 0.6) is comparable to that of θ-RbZn.…”

Magnetic and Electric Properties of Organic Conductors Probed by 13C-NMR Using Selective-Site Substituted Molecules

“…Salt with another packing arrangement, α-(BEDT-TTF) 2 X and θ-(BEDT-TTF) 2 X, has been a topic of interest due to the metal-insulator (MI) transition and charge disproportionation by off-site coulomb interaction [22][23][24][25][26][27][28][29]. In this type of organic conductor, various charge disproportionation patterns are realized, and these patterns give important information about the electronic structure.…”