Calculated band structure of a Bi2Te3(111) thin film of 5QLs with surface states marked as red

1. Spin Transfer in Spin-Orbit Coupled NanostructuresKyungwha Park, Virginia Polytech Institute and State University, DMR 0804665 Our research activity focuses on an understanding of spin transfer and spin-polarized electron transport in nanostructures where electron spin and orbital degrees of freedom significantly couple to each other. • One such nanostructure is a molecular junction consisting of single-molecule magnet (SMM) Mn12 bridged between gold electrodes. In addition to spin filtering (reported last year), we found that the degree of spin filtering greatly depends on interface geometry. A particular Mn12 orientation relative to the electrodes shown in Fig.1 provides several orders of magnitude greater spin-filtering ratios than other orientations, which would be useful for device applications including SMMs. We also show that current through Mn12 increases by an order of magnitude for gold-carbon bonding compared to typical gold-sulfur bonding at the interface. • Another such nanostructure is a ultra-thin film topological insulator (Bi2Te3). We find that topological nature of the surface states remains robust with the film thickness, and that the films of three or more quintuple layers (QLs) have topologically protected surface states. This agrees with experiments. Current vs voltage for Mn12 bridged between gold electrodes via gold-sulfur or gold-carbon bonding at the interface. Calculated band structure of a Bi2Te3(111) thin film of 5QLs with surface states marked as red

2. Spin Transfer in Spin-Orbit Coupled Nanostructures Kyungwha Park, Virginia Polytech Institute and State University, DMR 0804665 • The results for electron transport through the SMM Mn12 were obtained in collaboration with a former postdoctoral researcher (Barraza-Lopez) and a scientist (Ferrer) in Oviedo, Spain and a scientist (Garcia-Suarez) in Lancaster, UK. • We developed the method of identification of surface states and their topological nature in thin films of topological insulators. This method will be useful to build hybrid structures including topological insulator for device applications. • Trained one female graduate student (Linjun Li) and one female undergraduate student (Kristen Brown) for the research project. • Co-organized CECAM Workshop: Transport Phenomena in Molecular Nanostructures, CECAM-ETHZ, Zurich, Switzerland, June 22-25, 2010 with Prof. Evers (Karlsruhe, Germany) and Dr. Frederiksen (DIPC, Spain). • Presented results in conferences, workshops, and academic institutions in the States, Mexico, Europe, and South Korea. Training of students and a former postdoc International collaborations Research outcomes Giving seminars Organization of international workshop