Broadly, our research focuses on the epitaxial growth of complex oxide thin films and heterostructures in the pursuit to uncover, understand, and engineer new electronic phenomena and to push the frontier of technology with next generation devices based on these materials. The complex oxides offer an extremely wide range of properties not observed in conventional compound semiconductors and, thus, are an exciting playground for investigating or tailoring exotic phenomena and exploiting the unusual behavior in devices. Particular interest resides in interface, spin, structure, and charge effects that occur in layered structures with ferroic (and antiferroic) materials, such as (anti)ferromagnets, (anti)ferroelectrics, and multiferroics.
Some specific topics:
Magnetoelectric Switching in Thin Film Multiferroic Heterostructures
Multiferroic heterostructures are on a trajectory to impact spintronics applications through the significantly reduced energy consumption per unit area for magnetization switching (1 – 500 μJ cm-2) when compared to of current-driven magnetization switching (0.2 – 10 mJ cm-2). Considering this potential impact, it becomes necessary to understand converse magnetoelectric switching (electric field control of magnetism) and demonstrate this performance at scale. We focus on two categories of magnetoelectric/multiferroic systems: single-phase materials in exchange coupled heterostructures and composite systems (Ferroelectric/Ferromagnet) where the magnetoelectricity is mediated by strain.
Our objective is to understand fundamental magnetoelectric switching in these systems and to demonstrate low energy consumption for next generation computational technologies. We use thin film epitaxy, interfaces, strain, and novel materials investigate magnetoelectric switching in magnetoelectric heterostructures for tailored application. We develop devices and transport techniques to investigate magnetoelectric switching in configuration compatible with nanoelectronics. Further, we employ and develop scanning probe microscopy techniques to understand the kinetics of magnetoelectric switching, influence of boundary effects, and domain correlations.
Entropy-stabilized oxides emerge due to a large configurational entropy from multi-cation disorder as opposed to enthalpy of formation. Entropic stabilization enables the synthesis and exploration of oxide materials with compositions that have been considered to be unfeasible and the ability to include cationic species in typically unfavorable coordinations. Our objective is to understand the synthesis of thin film entropy-stabilized oxides and explain how the fundamental disorder and frustration of species, charge, structure, and spin emerge in the electromagnetic properties to enable design of new extremes in functional behavior. We leverage high energy physical vapor deposition methods, epitaxial strain, and composition to elucidate fundamental disorder-property correlations in single crystal entropy-stabilized oxide thin films.
Spin and Charge Transport in Antiferromagnetic Thin Film Heterostructures
Antiferromagnetic films are an attractive candidate for spin based nanoelectronics due to the absence of fringe fields, robustness to magnetic field, and efficient switching operation into the THz regime. We are investigating antiferromagnetic systems with strong spin orbit coupling and non-collinear spin order. These systems are capable of efficient spin current generation and have non-trivial transport physics due to their spin structure. We use thin film epitaxy to create new antiferromagnetic thin film heterostructures with distinct or tunable symmetry. Our objective is to probe the role of symmetry breaking, whether by spin or crystal structure, to understand the relationship between charge and spin in these materials.
Point Defects in Oxides
The functional properties of materials can be engineered by defects and impurities. First-principles calculations can serve as a powerful tool to predict properties of defects, e.g., atomic structure of defects, formation energy of defects, defect energy levels, diffusion mechanisms, and many other defect-related thermodynamic concepts. In collaboration with Prof. Kioupakis, we theoretically model point defects in oxides using first-principles calculations. Our objective is to develop strategies for doping of high band gap oxides and the role of point defects in the stabilization and strain relaxation of thin film entropy-stabilized oxides. Using our thin film capabilities, we control composition, stoichiometry, and strain and probe the evolution of electronic and lattice structure using dielectric X-ray spectroscopy techniques.
Spin-Valley Transport Phenomena in Transition Metal Dichalcogenides
Monolayer transition metal dichalcogenides (TMD) feature a reduced symmetry and strong spin orbit coupling. This combination results in spin and charge transport physics that is robust against thermal and electromagnetic perturbations, leading to long spin relaxation times and lengths. The low dimensionality in the vertical direction and semiconducting behavior also enable possibilities for electrically tunable spin transport. We leverage geometric and pressure control of plasma kinetics in PVD deposition techniques to realize magnetic heterostructures with monolayer TMDs. Our objective is to understand the interaction between magnetic systems and monolayer TMDs and to probe spin transport physics in these materials.