Third-order Electrical Conductivity of the Charge-ordered Organic Salt $\alpha$-(BEDT-TTF)${}_2$I${}_3$

Abstract

We performed third-order electrical conductivity measurements on the organic conductor $\alpha$-(BEDT-TTF)${}_2$I${}_3$ using an ac bridge technique sensitive to nonlinear signals. Third-order conductance $G_3$ is clearly observed even at low electric fields, and interestingly, $G_3$ is critically enhanced above the charge-order transition temperature $T_{\mathrm{CO}}=136$~K. The observed frequency dependence of $G_3$ is incompatible with a percolation model, in which a Joule heating in a random resistor network is relevant to the nonlinear conduction. We instead argue the nonlinearity of the relaxation time according to a phenomenological model on the mobility in materials with large dielectric constants, and find that the third-order conductance $G_3$ corresponds to the third-order electric susceptibility ${\chi }_3$. Since the nonlinear susceptibility is known as a probe for higher-order multipole ordering, the present observation of the divergent behavior of $G_3$ above $T_{\mathrm{CO}}$ reveals an underlying quadrupole instability at the charge-order transition of the organic system.

5 pages, 3 figures

References in corpus (7)

• Charge Ordering in alpha-(BEDT-TTF)2I3 by synchrotron x-ray diffraction
• Theoretical Aspects of Charge Ordering in Molecular Conductors
• Effects of the Zero-Mode Landau Level on Inter-Layer Magnetoresistance in Multilayer Massless Dirac Fermion Systems
• Optical freezing of charge motion in an organic conductor
• Molecular Quantum Materials: Electronic Phases and Charge Dynamics in Two-Dimensional Organic Solids
• Ferroelectric properties of charge-ordered alpha-(BEDT-TTF)2I3
• Possible Nonlinear Anomalous Thermoelectric Effect in Organic Massive Dirac Fermion System