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

Abstract

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 α-(BEDT-TTF)2I3 and α-(BETS)2I3. We observed ambipolar field effects in both compounds where both electron and hole doping (up to the order of 1013 cm−2) reduces the resistance by the band filling shift from the commensurate value. The maximum field-effect mobilities are approximately 10 and 55 cm2/Vs, and the gate-induced conductivities are 0.96 and 3.6 e2/h in α-(BEDT-TTF)2I3 and α-(BETS)2I3, respectively. However, gate-induced metallic conduction does not emerge. The gate voltage dependence of the activation energy in α-(BEDT-TTF)2I3 and the Hall resistance in α-(BETS)2I3 imply that the electric double layer doping in the present experimental setup induces hopping transport rather than band-like two-dimensional transport.

Sub-Band Filling, Mott-like Transitions, and Ion Size Effects in C60 Single Crystal Electric Double Layer Transistors

“…Researchers have demonstrated gate-induced insulator-to-metal transitions (IMTs), superconductivity, or ferromagnetism in EDLTs based on metal oxides, − metal sulfides, − and 2D materials such as graphene, , tellurene, , and MoS 2 . EDLTs have also been employed to examine charge ordering phenomena, Mott physics, and very recently an IMT in organic conductors. − Here we report EDLT measurements on single crystals of the well-known organic semiconductor C 60 , Figure a. C 60 is an intriguing choice for EDLT transport measurements as it is known to undergo a chemical doping-induced IMT and a metal-to-superconductor transition at 3 electrons/molecule. − Because C 60 is a large molecule (radius r C60 = 0.35 nm), the molecular density of the (111) close-packed plane of face centered cubic (FCC) C 60 crystals is relatively low at 1.1 × 10 14 cm –2 , which is comparable to the achievable 2D charge densities in EDLTs.…”

Organic Conductors

“…• Kawasugi et al reported doping effects using field-effect transistors consisting of electric double layers of charge-ordered insulators, α-(BEDT-TTF) 2 I 3 , and α-(BETS) 2 I 3 [24].…”