Materials Science Research Lecture
NOTE: Every student or postdoc (any option!) will receive a $5 SmartCash "coffee credit" for each Materials Research lecture attended in person. The credits will be tallied and issued after the last speaker of the term. ***Be sure to put your name on the sign-in sheet so you are counted.
Controlling electronic properties via bandstructure engineering is at the heart of modern semiconductor devices. We have extended this concept to semimetals utilizing confined thin film geometries and hetero-epitaxial interfaces to engineer electronic structure in rare-earth monopnictide and half-Heusler semimetallic systems. In the case of the rare-earth monopnictide, LuSb, quantum confinement changes the carrier compensation and differentially affects the mobility of the electron and hole-like carriers resulting in a strong modification in its large, non-saturating magnetoresistance behavior. Bonding mismatch at the heteroepitaxial interface of the semi-metal (LuSb) and a semiconductor (GaSb) leads to the emergence of a novel, two-dimensional, interfacial hole gas and is accompanied by a charge transfer across the interface that provides additional avenues to modify the electronic structure and magnetotransport properties in the ultra-thin limit.
The prediction and observation of topological surface states in half-Heusler compounds raises exciting possibilities to realize exotic electronic states and novel devices by exploiting their multifunctional nature. However, their position with respect to the Fermi level and the high density of bulk carriers have made it difficult to detect them through transport measurements. Here, we introduce compensation doping in epitaxial PtLuSb thin films as an effective route to tune the chemical potential and simultaneously reduce the bulk carrier concentration by more than two orders of magnitude compared to the parent compound. Linear magnetoresistance is shown to appear as a precursor phase of a quantum Hall-like phase potentially arising from the topological surface states on further reduction of the coupling between the surface states and the bulk carriers. Our approach paves the way to both reveal and manipulate exotic properties of topological phases in Heusler compounds.
More about the Speaker:
Chris Palmstrøm is a Professor in Electrical and Computer Engineering and the Materials Departments at the University of California, Santa Barbara. His research involves atomic level control and interface formation during molecular beam and chemical beam epitaxial growth of metallic compounds, metal oxides and compound semiconductors. He received his B.Sc. in physics and electronic engineering and Ph.D. in electrical and electronic engineering from the University of Leeds. After being a Lecturer in Norway and a Research Associate at Cornell, he joined Bellcore as a Member of Technical Staff in 1985. From 1994-2007 he was a Professor in the Department of Chemical Engineering and Materials Science at the University of Minnesota. In 2007 he joined the faculty at the University of California, Santa Barbara. He has pioneered dissimilar materials epitaxial growth studies using a combination of molecular beam epitaxial growth with in-situ surface science probes, and ex-situ structural and electronic characterization. He is a member of the Vannevar Bush Faculty Fellowship class of 2015 and is a Fellow of the AVS, APS, MRS and AAAS. He has received the North American MBE Innovator Award (2015) and the APS Adler Award (2018) and was made an Honorary Doctor at the Faculty of Engineering (LTH), Lund University (2018).