In-Depth Atomic Mapping of Polarization Switching in a Ferroelectric Field-Effect Transistor

The ferroelectric control of a Mott transistor is a promising strategy for nonvolatile low-power electronics. Understanding the fundamental limits of the ferroelectric-field effect is challenging, as the relevant length scales are restricted to a few atomic planes within the interface. Here, the polarization switching process of a prototypical ferroelectric Mott transistor combining BiFeO₃, a ferroelectric material with a large polarization, and (Ca,Ce)MnO₃, a charge-transfer insulator in which a few percent of Ce doping triggers a metal–insulator transition is investigated. While scanning probe microscopy indicates a complete switching of the ferroelectric gate, in-depth atomic-scale polarization mapping with scanning transmission electron microscopy reveals incomplete polarization reversal at the interface. Therefore, transport measurements show that the electronic properties of the Mott channel are virtually unchanged by the polarization direction. Nevertheless, in nanometer size areas where interfacial polarization switching occurs, dramatic changes of the electronic properties of (Ca,Ce)MnO₃ are revealed. These results indicate how the performance of mesoscale Mott devices is hindered, and at the same time reveal the possibility of nanoscale energy-efficient Mott transistors.