Special CM/AMO Seminar | Induced Superconductivity and Ferromagnetism in Topological Insulators, Speaker: Duming Zhang (Penn State)

Speaker: Duming Zhang (Penn State)

Topological insulators are interesting materials that have an insulating bulk band gap with conducting surface states. Exotic behaviors have been predicted when an energy gap (superconducting or magnetic) is induced at the surface. In this talk, I will discuss our recent experiments in this direction. First, I will demonstrate proximity-induced superconductivity in topological insulator (Bi2Se3) nanoribbons as a possible route towards the search for Majorana fermions in condensed matter [1]. We observe distinct signatures of the superconducting proximity effect, which might couple preferentially to a ballistic surface channel. In addition, we also provide evidence for possible formation of vortices in the proximity-induced region. Second, I will discuss our study on a magnetically-doped topological insulator (Mn-doped Bi2Se3) to induce a surface state gap [2], which might lead to exotic phenomena such as the topological magnetoelectric effect. Our systematic measurements reveal a close correlation between the onset of ferromagnetism and quantum corrections to diffusive transport, which cross over from the symplectic (weak anti-localization) to the unitary (weak localization) class. These observations are consistent with the prediction of a time-reversal symmetry breaking gap, which is further supported by angle-resolved photoemission spectroscopy measurements.

[1] Zhang, D. M. et al., “Superconducting proximity effect and possible evidence for Pearl vortices in a candidate topological insulator”, Phys. Rev. B 84, 165120 (2011).
[2] Zhang, D. M. et al., “Interplay between ferromagnetism, surface states, and quantum corrections in a magnetically-doped topological insulator”, submitted (2012).

Mr. Duming Zhang is a Ph. D. student from the Department of Physics at Penn State University. He received a B. S. in Applied Physics from Shanghai Jiao Tong University in China. He is now working with Prof. Nitin Samarth to synthesize high-quality semiconductor thin films and nanomaterials and to investigate their properties by electrical and optical measurements. His doctoral research focuses on understanding proximity-induced superconductivity and magnetism in topological insulators.