Two-Dimensional Electron Gases at Complex Oxide Interfaces

Susanne Stemmer, Professor, Materials Department, University of California Santa Barbara

Abstract: Two-dimensional electron gases at interfaces between two insulating oxides have attracted significant attention because they can exhibit unique properties, such as strong electron correlations, superconductivity and magnetism.  In this presentation, we will discuss an example for such an interface, between the strongly correlated Mott insulator GdTiO₃ and the band insulator SrTiO₃.  A fixed polar charge exists at these interfaces because of a polar discontinuity at the interface.  The interfacial charge can be compensated by a high-density, two-dimensional electron gas (2DEG).  At GdTiO₃/SrTiO₃ interfaces grown by molecular beam epitaxy, this results in a high-density 2DEG, of approximately 1/2 electron per surface unit cell, or 3×10¹⁴ cm^-2, for all GdTiO₃/SrTiO₃ heterostructures, independent of the individual layer thicknesses and growth sequences.  We will present measurements of quantum oscillations that provide insights into the nature of a 2DEG derived from the Ti d-states.  We will report on electron correlation effects, such as magnetism and mass enhancement, in extremely high carrier density SrTiO₃ quantum wells that can be obtained using these interfaces. Finally, we discuss the potential of oxide heterostructures for future electronic devices.  The work was done in collaboration with Pouya Moetakef, Clayton Jackson, Tyler Cain, Leon Balents, Jim Allen, Jimmy Williams and David Goldhaber-Gordon.

Speaker 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) and did her doctoral work at the Max-Planck Institute for Metals Research in Stuttgart (Germany).  She received her doctoral degree from the University of Stuttgart in 1995.  Following several postdoctoral positions she held an Assistant Professor position in Materials Science at Rice University from 1999 to 2002.  In 2002, she joined the University of California, Santa Barbara, where she was promoted to Full Professor in 2008.  Her research interests are in transmission electron microscopy techniques, in particular, the development of scanning transmission electron microscopy as a quantitative tool in materials science, novel dielectrics, oxide thin film growth and correlations between microstructure and electronic, dielectric and transport properties of oxide heterostructures.  She has authored or co-authored more than 150 publications.  Honors include an NSF Career Award, Fellow of the American Ceramic Society and Fellow of the American Physical Society.