Charge Transport in Charge-Ordered States of Two-Dimensional Organic Conductors, α-(BEDT-TTF)₂I₃ and α'-(BEDT-TTF)₂IBr₂

Abstract

Electric conductance and dielectric constant have been measured in the charge-ordered states of the quasi twodimensional organic conductors -(BEDT-TTF) 2 I 3 and 0 -(BEDT-TTF) 2 IBr 2 to understand the charge transport mechanism. The current-voltage (I-V ) characteristics show a strong nonlinear behavior, which is qualitatively explained by the transport of individual carriers thermally excited from the charge-ordered states in BEDT-TTF layers. The discrepancy with the simulation based on the thermal activation model at low temperatures is likely due to quantum tunneling through the potential barrier. The dielectric constants show a large difference between the in-plane and out-of-plane directions of the samples, showing a highly two-dimensional nature of Coulomb potential. The temperature dependence of dielectric constant is ascribed to the polarization effect of the thermally excited electronhole pairs, consistent with the model of nonlinear I-V characteristics. All these features are qualitatively the same between -(BEDT-TTF) 2 I 3 and 0 -(BEDT-TTF) 2 IBr 2 , despite the different structural and magnetic properties.

Dielectric spectroscopy on organic charge-transfer salts

“…The out-of-plane ε' spectra from ref. [24], shown in figure 16, qualitatively agree with the relaxor behaviour detected in [10]. Especially, ε' continuously increases with temperature for the investigated range 10 K < T < 50 K. Moreover, the frequency dependence may be consistent with relaxor ferroelectricity but the absolute values reached at low frequencies are clearly higher than in [10] pointing to sample-dependent differences or non-intrinsic effects.…”

“…In contrast to -(ET) 2 Cu[N(CN) 2 ]Cl and -(ET) 2 Cu 2 (CN) 3 , CO in this material is well established and recently relaxor behaviour was detected deep in the charge-ordered state [10]. Various dielectric investigations of this system exist and have been interpreted in different ways [10,11,24].…”

“…ning the abso proach a stat t, in figure 1 au at high fr spectra exten o-sample var amples that tric constant ectric consta ons [24]. Figure 17.…”

Kosterlitz-Thouless-Type Transition in a Charge Ordered State of the Layered Organic Conductorα−(BEDT−TTF)2I3Uji1, Kodama2, Sugii3 et al. 2013Phys. Rev. Lett.132190View full textAdd to dashboardCite

“…The dielectric constant of the BEDT-TTF layers is considerably larger than that of the anion layers. Therefore, the electric fluxes of thermally excited charges are confined in the BEDT-TTF layers [23][24][25]27,28]. Consequently, a long-range 2D Coulomb potential of the form lnðrÞ is realized in the BEDT-TTF layers.…”

Cooperative dynamics in charge-ordered state ofα-(BEDT-TTF)2I3

“…15,16 Further, an analogy to SDW sliding has been invoked to explain unusual nonlinear effects in the case of antiferromagnetic phase of localized spins in MDT-TS organic compound. 17 Finally, when the constant voltage is applied to the sample, current oscillations with very low fundamental frequencies (10-100 Hz) have been observed in the NDR region of several quasi-2D organics and interpreted as the switching frequency between low and high current states in analogy to the well-known Gunn effect observed in twovalley semiconductors.…”