Emergent Phenomena in Spatially Confined Manganites

Rare earth manganites exhibit colossal magnetoresistance (CMR). There is evidence that alloyed single crystal materials in this class can display electronic inhomogeneity in which areas with vastly different electronic and magnetic properties can form and coexist in phase separated domains ranging in size from a few nanometers to micrometers. This phase separation (PS) is of particular interest, as it has been suggested that it is the central feature that leads to CMR in manganites, the Mott transition in VO₂ and may play a role in high-TC superconductivity in cuprates. However there is debate as to its precise role.

The purpose of my research is to answer fundamental questions about the specific role of PS in complex oxides. I reduce single crystal thin films of an electronically phase separated manganite to the scale of their inherent electronic phase domains near the metal-insulator transition. Unlike transport measurements done on bulk or thin films where the electrons follow only the metallic path of least resistance, this configuration forces electrons to travel through both the metallic and insulating regions residing in the material. This has led to observations of several new phenomena such as a reemergent metal-insulator transition, ultra-sharp jumps in resistivity at the metal-insulator transition, and the first high resolution observation of single domain electronic phase transitions in the time domain.

While the manganites will be the primary focus throughout this dissertation, the spatial confinement techniques presented here are not limited to only these materials. They can be applied to any phase separated system to probe regions resistively hidden to transport measurements.