Control of emergent properties at a correlated oxide interface with graphene.

Electrolyte gating of complex oxides enables investigation of electronic phase boundaries and collective response to strong electric fields. The origin of large conductance modulations and associated emergent properties in such field effect structures is a matter of intense study due to competing contributions from electrostatic (charge accumulation) and electrochemical (crystal chemistry changes) effects. Vanadium dioxide (VO2) is a prototypical correlated insulator that shows an insulator-to-metal transition at ∼67 °C and recent studies have noted a vast range of electronic effects in electric double-layer transistors (EDLT). In this study, we demonstrate that the response of electrolyte gated VO2 devices can be deterministically controlled by inserting a monolayer of graphene at the oxide-electrolyte interface. Several electrolytes as well as dopants (such as lithium ions and protons) were employed in EDL transistors to show that graphene serves as an inert barrier that successfully protects the oxide surface from chemical reactions. This monolayer interface has a striking effect on resistance modulation in the vanadium dioxide transistor channel up to several orders of magnitude and enables retention of the insulating phase. The studies allow new insights into the response of correlated insulators in EDLTs and inform design of correlated oxide-2D heterostructures for electronics and sensors.