Ambipolar gate effect and low temperature magnetoresistance of ultrathin La_0.8Ca_0.2MnO₃ films

Ultrathin La_0.8Ca_0.2MnO₃ films have been measured in a field-effect geometry. The gate electric field produces a significant ambipolar decrease in resistance at low temperatures. This is attributed to the development of a pseudogap in the density of states and the coupling of localized charge to strain. Within a mixed phase scenario, the gate effect and magnetoresistance are interpreted in the framework of a "general susceptibility," which describes how phase boundaries move through a hierarchical pinning landscape.