What is Mott-insulator?

 Our focus concentrates in Mott-insulators in which Coulomb interaction among carriers blocks metallic transport. In this strongly correlated situation of charge carriers, Mott insulator stays in a fragile semiconducting state, where carrier injection, chemical and/or physical pressure (or strain), and thermal fluctuation can drive it into a metallic state by phase transition (i.e. Mott transition: Figure below). Since the carrier density (band-filling) of a FET interface can be finely modulated by an electrostatic field from the gate electrode, it is anticipated that the Mott-insulating state can be switched to a metallic state by a field effect. Indeed, our previous work showed such an insulator-to-metal transition in terms of the band structure, and these results provide not only a possibility of application use of organic Mott-FET but also a significant insight into the mechanism of Mott transition itself. We are now expanding our research target both to the superconducting transition of Mott-FET and to its room-temperature operation.

Figure. Concept of a Mott-insulator (center) along with its bandfilling-controlled (left) and bandwidth-controlled (right) Mott transitions. When the band is half-filled and band energy is small, the carriers are localized because of on-site Coulomb interaction (U). This situation is broken down either by changing the carrier concentration or by compressing the lattice. In many cases, the Mott transitions are associated with superconductivity at the boundary between metallic and insulating phases.