ABSTACT
Novel Synthesis of Quantum Epitaxial Heterostructures by Design
Chang-Beom Eom
University of Wisconsin-Madison
Quantum materials are setting the framework for technological advances. Their novel properties are opening new directions for electronics, spintronics, and magnetics. The most important avenues require thin film materials for microelectronic devices, stacked into heterostructures of disparate materials to provide new functionalities. We develop novel synthesis routes for a new generation of epitaxial quantum thin film heterostructures only millionths of millimeters thick, pursuing fundamental science for development of new applications. We synthesize films that are of comparable or higher quality than available bulk single crystals, but more importantly can be maintained far from equilibrium, so that phases that don’t exist naturally can be obtained by epitaxial stabilization of thin films through a controlled interaction with the substrate that supports them.
But these novel systems are usually sensitive to the growth substrate, composition and defects, and the challenge of forming atomically perfect interfaces. We design substrate interactions, then identify and control point defects, to create atomic interfaces perfect enough to reveal new phenomena and discover fundamental intrinsic properties of quantum materials arising from dimensionality, anisotropy, and electronic correlations. We have developed a unique free-standing oxide stacked membrane fabrication technique that can apply large dynamic strain to novel layered systems. We implement a Hybrid Pulsed Laser Deposition (HPLD), and begin to understand routes to new discoveries through control of highly perfect and defect free films and heterostructures. Our thrusts expand into new materials systems:
Fabrication of Novel Quantum Material Platforms
Novel Hybrid PLD Synthesis Route – We continue to develop hybrid PLD, in particular for Niobium doping of KTaO3 (KTO), a material with a quantum critical point. We have demonstrated that this ferroelectric quantum critical point can be controlled by Nb doping and strain, possible only with thin films. We have demonstrated that our hybrid PLD synthesizes uniquely high-quality synthesis KTO thin film membranes for assembly into stacked heterostructures.
Complex oxide membranes We develop a registry design synthesis approach for moiré heterostructures stacked from freestanding thin film membranes twisted around their crystal axes. This expansion of quantum heteromaterials assembles membranes into twisted heterostructures of complex oxide and nitride materials.
Fundamental Science of Novel Quantum Materials Platform
LaAlO3/KTaO3 interface superconductivity – We use Nb doping and electrostatic gating to move this heterostructure to the quantum critical point, enhancing superconductivity. We will also use dynamic strain of KTO membranes to understand the role of the quantum critical point in KTO superconductivity.
Strain controlled twisted oxide membranes heterostructures - We will investigate structural, electronic, and magnetic phenomena in different types of moiré heterostructures. We will investigate 2D charge localization, 2D polarization-vortex crystals, and topological spin textures at twisted oxide interfaces
Ba(PbxBi1-x)O3 superconducting films and membranes with strong spin-orbit coupling –We have shown that BPBO shows strong spintronic effects and high-temperature superconductivity. We will heterostructure BPBO by assembling membranes into complex spintronic heterostructures.
This research involves close collaboration with theory, computation, and state-of-the-art structural, electronic, magnetic, and transport characterizations to challenge many exciting fundamental scientific issues. We expect this research to lead to discovery of new quantum materials, and to exploration of emergent phenomena for technological applications.
