Asymmetric phase transitions observed at the interface of a field-effect transistor based on an organic mott insulator

A high-quality field-effect transistor (FET) with an organic Mott insulating channel was fabricated, and its low-temperature transport properties were measured at various gate voltages (V_G). The resistance of the FET showed a clear ambipolar field effect as well as a sudden drop in both the p-type and n-type regions, the areas of which merged into one at lower temperatures. These drops in the resistance were attributed to Mott transitions that were induced by electrostatic doping into the FET interface. The n-type transition started to appear at higher temperatures but showed a relatively narrow V_G range relative to that of the p-type transition. These results are suggestive of electron-hole asymmetry of the Mott-insulator-to-metal or Mott-insulator-to-superconductor transitions in the doped organic correlated materials. A strain on the device was also evaluated by X-ray diffraction.