Low‐Frequency Charge Carrier Dynamics in Ferroelectric κ‐(BEDT‐TTF)2X – A Comparative Study of X = Cu[N(CN)2]Cl and X = Hg(SCN)2Cl

Abstract

This paper presents a comparative study of the low‐frequency charge carrier fluctuations of κ‐(ET)2Cu[N(CN)2]Cl (κ‐Cl) and κ‐(ET)2Hg(SCN)2Cl (κ‐Hg‐Cl), two organic charge‐transfer salts exhibiting a Mott‐insulating and charge‐ordered ground state, respectively, accompanied by ferroelectric order. For κ‐Cl, pronounced random telegraph signals are found, which are enhanced over the 1/f‐background fluctuations at characteristic temperatures where changes of either the structural or the electronic dynamics occur. From the shift of the characteristic frequencies with temperature, the corresponding activation energies are extracted. The switching of polar nanoregions related to relaxor ferroelectricity of the investigated sample is suggested as origin of the observed transport dynamics around TFE. For κ‐Hg‐Cl (showing long‐range ferroelectric order accompanied by a charge ordering metal–insulator transition), strong changes and a sharp peak in the low‐frequency fluctuations at TMI are found. For this compound also, spatially correlated and electric field‐dependent fluctuations are observed in the ferroelectric phase.