Engineering complex oxide interfaces for oxide electronics

A complex interplay of physics and chemistry in transition metal oxides determines their electronic, magnetic, and ferroic properties enabling a wide range of applications of these materials. BiFeO_3, a canonical multiferroic system exhibits the interesting feature of enhanced conductivity on ferroelectric domain walls, in an otherwise insulating surface. Although it attracted much interest, many aspects regarding its origin and magnetic behavior are not fully understood; particularly at interfaces with different buffer layers; raising open questions on the linkage between electronic properties to its intrinsic order parameters like structure and symmetry. Conventionally, BiFeO_3 has been grown on a conducting bottom electrode of SrRuO_3 whose thickness again dictates the density of the domain walls. In order to probe these ferroelectric domain walls in a current perpendicular to plane configuration using a novel technique; namely Ballistic Electron Emission Mmicroscope (BEEM), it was imperative to first electrically characterize the interface between metallic SrRuO_3 and the substrate (Nb:SrTiO_3). We start our studies with the SrRuO_3/Nb:SrTiO_3 interface where we establish the strong inter-relation between geometrical and electronic structure at the heterointerface across phase transition, and engineer the electronic properties of these heterointerfaces. Further on, we investigated the influence of bulk polarization state provided by the underlying substrate termination, to hot electron transmission in BiFeO_3. Additionally, by designing a variant of BEEM we demonstrate that this technique potentially scores over the conventional scanning probe techniques used so far. This cates a novel route to study the nanoscopic ferroelectric domain walls of BiFeO_3 thin films.