Increase in electron mobility as a function of strain in SrTiO 3 films.

1. Giant Enhancement of Electron Mobility in SrTiO3 Using StrainSusanne Stemmer, University of California, Santa Barbara, DMR 1006640 • Engineering of charge carrier mobilities using strainis widely used for semiconductors, including the latest generations of silicon transistors. • Complex oxide thin films, such as SrTiO3,are typically grown by methods that produce defect densities that are too high to allow for the study of strain effects on carrier transport. • In this program, SrTiO3 is grown by molecular beam epitaxy (MBE), allowing for orders of magnitude lower defect densities. Using MBE-grown SrTiO3, we have shown dramatic enhancements in the electron mobility of SrTiO3 under strain. The mobility increased by more than 300%, to values greater than 120,000 cm2V-1s-1, far exceeding the largest values ever reported. These very large mobilities will expose quantum transport in a materials system that is fundamentally different from semiconductors. Photo (left) and schematic (right) of the three-point bending apparatus used to measure the mobility of SrTiO3 thin films as a function of strain. B. Jalan, S. J. Allen, G. E. Beltz, P. Moetakef, S. Stemmer, Appl. Phys. Lett. 98, 132102 (2011). Increase in electron mobility as a function of strain in SrTiO3 films.

2. Undergraduate Research and Interdisciplinary CollaborationSusanne Stemmer, University of California, Santa Barbara, DMR-1006640 • A major aspect of the project is that the high-quality materials grown in the project enable multidisciplinary collaborations, involving faculty, graduate and undergraduate students in physics who study the transport physics and materials scientists, who develop the materials and heterostructures. Most of the publications from this project have co-authors from several departments. • Shown on the left is UCSB undergraduate James Kally, who works on tunneling experiments using the complex oxide thin films grown in this program. UCSB Physics senior James Kally with the low-temperature transport measurement system he uses for tunneling studies of complex oxide heterostructures.