Hysteretic Current–Voltage Characteristics in the Deuterium-Dynamics-Triggered Charge-Ordered Phase of κ-D₃(Cat-EDT-TTF)₂

Abstract

A purely organic material, κ-D3(Cat-EDT-TTF)2, undergoes a peculiar charge ordering transition triggered by deuterium localization in hydrogen bonds between two-dimensional conducting layers. Here, we report that the current density–electric field characteristics of this charge-ordered phase exhibit negative differential resistance and also hysteresis, which is considered to be induced by the deuterium dynamics. Upon the application of a pulsed voltage, the resistance irreversibly changes; namely, the initial charge-ordered state is changed to a metastable state through a high-conducting (excited) state, which results in the appearance of the hysteresis. Raman spectroscopy suggests that this metastable state is a non-charge-ordered dimer-Mott state. Interestingly, this state does not appear at low temperatures, and instead, the initial charge-ordered state reappears. These results are well understood by considering the temperature-dependent dynamics of hydrogen-bonded deuterium (i.e., localization/fluctuations) coupled to the π-electrons in the conducting layers. In contrast, the hydrogen analogue κ-H3(Cat-EDT-TTF)2, which is a dimer-Mott insulator without proton localization, does not show such hysteretic behavior.