Epitaxy with a Twist—Magnetotransport Phenomena in Oxide Heterostructure Interfaces

Complex metal oxides are an exciting class of electronic materials which share key properties with conventional semiconductors but also bring new intrinsic functionalities to the world of electronics: high-temperature superconductivity, insulator transitions, ferromagnetism, ferroelectricity, piezoelectricity, and multiferroic properties. This richness arises from a strong correlation between the electrons in the <i>d</i> orbitals, which gives rise to a complex interplay between the charge, spin, orbital, and lattice degrees of freedom. Traditionally, complex metal oxides can only be grown epitaxially on a lattice-matched substrate. However, the advent of lattice-matched sacrificial layers for complex metal oxides has overcome this limitation, allowing for the fabrication of freestanding complex oxide membranes. By reassembling complex oxide freestanding membranes with different materials and orientations into artificial stacks, it is possible to bypass the epitaxial roadblocks. An additional degree of freedom is introduced in such artificial stacks: by twisting the layers one can synthesize moiré superlattices.<br/><br/>In this work, we present our approach to prepare novel interfaces between two controlled twisted and stacked freestanding membranes using SrTiO3-based materials. We start with a SrTiO3-based thin film epitaxially grown on a Sr3Al2O6 sacrificial layer that dissolves in water. After dissolving the layer, we transfer the released membrane onto a new substrate. Next, we stack a second membrane at an angle to the first, creating a unique, twisted interface between the two membranes. This method results in defect-free heterostructures of freestanding oxide membranes at the interface. This approach facilitates the direct integration of complex oxides at any desired twist angle, which we utilized to conduct low-temperature transport studies across a twisted bilayer freestanding oxide junction device.