Liu Ying: Studying Dirac materials : graphene and topological insulator (Bi2Se3)
Liu Ying, University of Wisconsin, Milwaukee
Dec 19, 2012
from 12:00 PM to 01:00 PM
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We focus on the MBE growth and in situ characterization of Dirac materials, graphene and topological insulators. Epitaxial graphene forms with the diffusion and desorption of Si from SiC. Combining DFT calculations and STM study, a novel Si diffuse dynamic process was proposed, which involves Si vertical diffusion with an energy barrier comparable to Si lateral diffusion. Artificial defects created by Ar plasma show a bi-stability mode with two types of scatters, exhibiting different behaviors for scattering electrons. And the electrical field generated by STM tip could switch the two states, realizing the manipulation of the mobility of Dirac electrons at atomic scale. In addition, high quality graphene film provides a good starting surface for topological insulator growth. The epitaxy of Bi2Se3 on graphene shows different behavior due to the weak van der Waals force, which developed a novel model for the layered materials growth. However, the surface of Bi2Se3 is quite fragile and can be easily destroyed, even in UHV. By studying the reaction of the surface with a few different gases in controlled environments, the factors leading to the surface degradation were determined. In the end of the talk, fabricating topological insulator heterostructures for protecting the surface was proposed. Our future work will focus on the heteroepitaxy of topological insulators on superconductors, in order to create non-Abelian Majorana states at the topological insulator/superconductor interface for quantum computing purposes.
 “A novel Si diffusion path for pit-free graphene growth on SiC(0001)”, G. F. Sun, Y. Liu, S. H. Rhim, Y. Qi, J. F. Jia, Q. -K. Xue, M. Weinert, and L. Li, Phys. Rev. B 84, 195455 (2011).
 “Spiral growth without dislocations: Molecular beam epitaxy of the topological insulator Bi2Se3 on epitaxial graphene/SiC(0001)”, Y. Liu, M. Weinert, and L. Li, Phys. Rev. Lett 108, 115501 (2012).