1. Condensed-Matter Physics & Materials Science Seminar

    "First-principles studies of topological insulator and ferroelectric oxide interfaces"

    Presented by Weidong Luo, Department of Physics and Institute of Natural Sciences, Shanghai Jiao Tong University, Shanghai 200240, China

    Monday, March 25, 2013, 11 am
    Bldg. 735 Conf. room A

    Hosted by: Jing Tao

    In the first part of the talk, I present our recent study of the topological surface states in heterostructures formed by a topological insulator (TI) and a magnetic insulator (MI). Several MIs with compatible magnetic structure and relatively good lattice matching with TIs are identified, and the best candidate material is found to be MnSe, an anti-ferromagnetic insulator. We perform first-principles calculations in Bi2Se3/MnSe superlattices and obtain the surface state bandstructure. The magnetic exchange coupling with MnSe induces a gap of 54 meV at the Dirac surface states of Bi2Se3. In addition we tune the distance between Mn ions and TI surface to study the distance dependence of the exchange coupling. Finally, we study the band bending effect at the Bi2Se3/MnSe interface, and propose possible solutions to the problem [1]. In the second part of the talk, I present the work on interfaces of ferroelectric materials, namely BiFeO3 (BFO) and PbTiO3 (PTO). In the case of BFO interfaces, we study how much the interfacial valence mismatch affect the electrostatic potential step across the interface, which manifests itself as the biased-voltage in ferroelectric hysteresis loops and determines the ferroelectric state [2]. In the case of PTO interfaces, we investigate using density functional theory, in combination with electron microscopy, to show how the ferroelectric interfaces cope with the need to terminate ferroelectric polarization [3]. [1] W. Luo and X.-L. Qi, Phys. Rev. B 87, 085431 (2013). [2] P. Yu, W. Luo, D. Yi et al, Proc. Natl. Acad. Sci. USA 109, 9710 (2012). [3] M. F. Chisholm, W. Luo, M. P. Oxley, S. T. Pantelides, and H. N. Lee, Phys. Rev. Lett. 105, 197602 (2010).