The Response of Transport Properties to Static Electric Field in La $_{0.7}$ Ce $_{0.3}$ MnO

We investigated the influence of static electric field on the transport properties in La_0.7Ce_0.3MnO₃ epitaxial thin films by using a simple field effect configuration (FEC), which was formed on a single layer film. Substrates act as gates and films as channels. Such an easily manipulative technique avoids many possible problems appeared in multilayer structures, such as poor interface and severe inter-diffusion, which may influence the intrinsic characteristics of investigated targets. One knows that tetravalence-doped La_0.7Ce_0.3MnO₃ (LEMO) systems exhibit metal-insulator transition and ferromagnetic behavior, similar to the ditravalence-doped La_0.7Ca_0.3 MnO₃. However, for the conductive mechanism of LEMO, strong controversies have existed for a long time with whether it is intrinsically electron-type or hole-type. Our experiments give evidence of the hole-type nature in LEMO. In the device with LEMO as channel and LaAlO₃(LAO) as gate, applied positive bias poles gate and induces charge at the area between gate and channel. The polarized charge in the gate is compensated by inducing electrons in the channel. If LEMO is of electron-type, the increased carrier density would cause a decease of channel resistance. However, we experimentally found the channel resistance remarkably increases upon a positive bias. Such a fact is completely the same as the behavior observed in hole-doped La _0.7Ca_0.3MnO₃channel, and thus strongly supports the hole-type nature in LEMO channel. Furthermore, we found that the large field effect in LEMO is nonlinear and polarity dependent on the applied bias. A percolative phase separation picture is taking into account to interpret the observed field effect