Wednesday, November 15, 2017
4:00 pm
Spalding Laboratory 106 (Hartley Memorial Seminar Room)

Materials Science Research Lecture

Topological Heterostructures by Molecular Beam Epitaxy
Susanne Stemmer, Professor, Materials Department, UC Santa Barbara

Abstract: Topology, both in real space and in reciprocal space, has emerged as a new design principle for materials that can host a wealth of novel properties.  Examples of topological materials classes discovered over the past few years include three-dimensional topological insulators and three-dimensional Dirac semimetals.  Interfaces and heterostructures with three-dimensional topological materials offer opportunities to control and manipulate their electronic states and associated phenomena, for example, via electric field effect, strain, or symmetry breaking.  In this presentation, we will discuss recent progress in the growth of thin films of the three-dimensional Dirac semimetal Cd3As2 by molecular beam epitaxy.  We show that high-mobility, epitaxial Cd3As2 films can be grown on III-V substrates and discuss some of the phenomena that can be observed, such as an unusually large negative longitudinal magnetoresistance under parallel electric and magnetic fields.  These heterostructures allow for experimental tests of theoretically predicted transitions between topological states by manipulating parameters, such as confinement.  For example, as the film thickness is reduced, a band gap opens in the bulk Dirac electronic states and we observe the quantum Hall effect that is associated with gapless surface states.  If time permits, we will also discuss a completely different type of topological feature, magnetic skyrmions, and their potential realization in oxide thin film heterostructures.
This work was performed in collaboration with Timo Schumann, Manik Goyal, David Kealhofer, Luca Galletti, and Kaveh Ahadi.

Bio: Susanne Stemmer is Professor of Materials at the University of California, Santa Barbara.  She received her Diploma in Materials Science from the Friedrich-Alexander University Erlangen-Nürnberg (Germany).  She did her doctoral work at the Max-Planck Institute for Metals Research in Stuttgart (Germany) and received her doctoral degree from the University of Stuttgart in 1995.  Following postdoctoral positions, she held an Assistant Professor appointment in Materials Science at Rice University from 1999 to 2002.  In 2002, she joined the Materials Department of the University of California, Santa Barbara.  Her research interests are in the development of quantitative scanning transmission electron microscopy techniques, molecular beam epitaxy of new materials, and heterostructures of strongly correlated and functional oxides and topological materials.  She has authored or co-authored more than 230 publications.  Honors include election to Fellow of the American Ceramic Society, Fellow of the American Physical Society, Fellow of the Materials Research Society, Fellow of the Microscopy Society of America, and a Vannevar Bush Faculty Fellowship.

 

**Refreshments served at 3:30pm in the Spalding Laboratory Lobby.

Contact Jennifer Blankenship jennifer@caltech.edu at 626-395-8124
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