Electron transport in TTF-CA under High pressures

We investigate the electron transport in the neutral-ionic transition material, tetrathiafulvalene-p-chloranil (TTF-CA), under extremely high pressures up to 82.5 kbar, using a cubic anvil system. At room temperature, as pressure is applied, the resistivity steeply decreases in the neutral phase and exhibits a minimum followed by an increase, which reproduces the previously reported results. However, resistivity is found to become insensitive to pressure above 20 kbar, where the ionic phase is stabilized. The robust transport characteristics of the ionic phase is in contrast with the pressure-sensitive transport in the neutral phase. The temperature dependence of resistivity is insulating in the whole pressure range up to 82.5 kbar but shows breaks in the activation plot at certain temperatures, suggesting that some phase transition occurs in the ionic phase.