Electric Double Layer Doping of Charge-Ordered Insulators α-(BEDT-TTF)2I3 and α-(BETS)2I3

Field-effect transistors based on strongly correlated insulators are an excellent platform for studying the electronic phase transition and simultaneously developing phase transition transistors. Molecular conductors are suitable for phase transition transistors owing to the high tunability of the electronic states. Molecular Mott transistors show field-induced phase transitions including superconducting transitions. However, their application to charge-ordered insulators is limited. In this study, we fabricated electric double layer transistors based on quarter-filled charge-ordered insulators alpha-(BEDT-TTF)(2)I-3 and alpha-(BETS)(2)I-3. We observed ambipolar field effects in both compounds where both electron and hole doping (up to the order of 10(13) cm(-2)) reduces the resistance by the band filling shift from the commensurate value. The maximum field-effect mobilities are approximately 10 and 55 cm(2)/Vs, and the gate-induced conductivities are 0.96 and 3.6 e(2)/h in alpha-(BEDT-TTF)(2)I-3 and alpha-(BETS)(2)I-3, respectively. However, gate-induced metallic conduction does not emerge. The gate voltage dependence of the activation energy in alpha-(BEDT-TTF)(2)I-3 and the Hall resistance in alpha-(BETS)(2)I-3 imply that the electric double layer doping in the present experimental setup induces hopping transport rather than band-like two-dimensional transport.