Tunable Metallic Conductivity in Ferroelectric Nanodomains

Domain wall conductivity in ferroelectric and multiferroic oxides is an essential example of new electronic properties created by topological defects. So far electron transport through domain walls in canonical BiFeO$_{3}$ and PbZr$_{0.2}$Ti$_{0.8}$O$_{3}$ (PZT) ferroelectrics has been dominated by thermally activated hopping, concealing the enabling physics and limiting potential applications. We will present a pioneering observation of metallic conductivity in nanoscale ferroelectric domains in PZT, that unambiguously identifies a new conduction channel created through the bulk of the oxide film [1]. From a corollary theoretical analysis, we conclude that metallic conductance is enabled by the interplay of charging and flexoelectric effects at tilted and curved walls of the nanodomain. Furthermore, both type and density of carriers can be tuned by manipulation of the order parameter. Thus, a new family of electronic properties may be found in multiferroic and topologically nanostructured complex oxides. [1] Maksymovych et al, \textit{Nano Lett}. in review (2011). Research conducted at the Center for Nanophase Materials Sciences, sponsored by BES, U. S. DOE.