Ferroelectric control of Mott insulators at nanometer/nanosecond scales – FERROMON

Controlling strongly-correlated electronic states and inducing metal/insulator transitions by electric-field effect is the key objective of Mott-tronics (named after Nobel Prize laureate Sir Neville Mott). Conceptualized by IBM in the late 1990's, Mott transistors could surpass conventional MOSFETs in terms of ON/OFF ratios and power consumption. With ferroelectric gates, they could also lead to fast and high-endurance non volatile memories. Attempts to realize such devices have culminated with the recent report (Tokura’s group at Riken in Japan, Nature 2012) of a field-effect induced metal-insulator transition in VO2 thin films gated with ionic liquids. However, a subsequent study (Parkin’s group at IBM in the US, Science 2013) concluded that extrinsic, voltage-induced oxygen vacancy motion rather than intrinsic electrostatic effects was responsible for the large resistance change, raising controversy over such ionic liquid gated VO2 transistors.

Two key challenges must be addressed to meet the long-standing goal in Mott-tronics of a non volatile, reversible, electronically-driven transition between a metallic and an insulating state: (i) identify a channel material in which a metal-insulator transition occurs at very low doping level; (ii) combine it with a switchable gate material capable of accumulating and depleting large carrier densities.

FERROMON will address both challenges and investigate a model system consisting of epitaxial perovskite heterostructures combining a Mott insulator, (Ca,Ce)MnO3, with a (magnetic) ferroelectric, BiFeO3. BiFeO3/(Ca,Ce)MnO3 bilayers are of high crystalline quality and we recently demonstrated a large electrical response at room temperature induced by ferroelectric switching in both planar and vertical devices. The rich phase diagram of (Ca,Ce)MnO3 offers great potential for new exciting effects where ferroelectric field effect could not only drive metal/insulator but also magnetic phase transitions.

In this framework, I will dedicate my 7-year experience with significant achievements in the field of oxide interfaces, nanoscale ferroelectrics, interface magnetoelectric coupling and ferroelectric devices to conduct the project with three main objectives:
- Drive electronic and/or magnetic phase transitions in strongly correlated oxides by ferroelectric field effect
- Understand at the atomic level the interplay between ferroelectricity and electronic properties at oxide interfaces
- Exploit ferroelectric domain dynamics to control electronic and/or magnetic properties at the ns scale.