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We report the nonvolatile modulation of microwave conductivity in ferroelectric PbZr0.2Ti0.8O3-gated ultrathin LaNiO3/La0.67Sr0.33MnO3 correlated oxide channel visualized by microwave impedance microscopy. Polarization switching is obtained by applying a tip bias above the coercive voltage of the ferroelectric layer. The microwave conductivity of the correlated channel underneath the up- and down-polarized domains has been quantified by finite-element analysis of the tip-sample admittance. At room temperature, a resistance on/off ratio above 100 between the two polarization states is sustained at frequencies up to 1 GHz, which starts to drop at higher frequencies. The frequence-dependence suggests that the conductance modulation originates from ferroelectric field-effect control of carrier density. The modulation is nonvolatile, remaining stable after 6 months of domain writing. Our work is significant for potential applications of oxide-based ferroelectric field-effect transistors in high-frequency nanoelectronics and spintronics. 

We report the implementation of a dilution refrigerator-based scanning microwave impedance microscope with a base temperature of ∼100 mK. The vibration noise of our apparatus with tuning-fork feedback control is as low as 1 nm. Using this setup, we have demonstrated the imaging of quantum anomalous Hall states in magnetically (Cr and V) doped (Bi, Sb)2Te3 thin films grown on mica substrates. Both the conductive edge modes and topological phase transitions near the coercive fields of Cr- and V-doped layers are visualized in the field-dependent results. Our study establishes the experimental platform for investigating nanoscale quantum phenomena at ultralow temperatures.