Electroresistance and Electronic Phase Separation in Mixed-Valent Manganites

The sensitivity of transport in colossal magnetoresistance (CMR) manganites to external electric and magnetic fields is examined using field effect configurations with ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_3$ (LCMO), ${\mathrm{Na}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_3$, ${\mathrm{La}}_{0.7}{\mathrm{Ba}}_{0.3}{\mathrm{MnO}}_3$, and ${\mathrm{La}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_3$ (0.5-doped LCMO) channels, and ferroelectric ${\mathrm{PbZr}}_{0.2}{\mathrm{Ti}}_{0.8}{\mathrm{O}}_3$ (PZT) or dielectric $\left({\mathrm{SrTiO}}_3\right)$ gates. A large electroresistance (ER) of $\sim 76\%$ at $4\times {10}^5\mathrm{V}/\mathrm{cm}$ is found in LCMO with PZT-ferroelectric gate, but the magnitude of the effect is much smaller (a few percent) in the other three channels. The ER and CMR effects are remarkably complimentary. The size and systematics of the effect strongly favor a percolative phase separation picture.