Proximity and gating effects of a topological insulator and an s-wave superconductor in Bi2Se3-NbN thin film bilayers

In recent years we have been involved in the search for Majorana fermions (MF) in topological superconducting thin films [1-3]. The idea was to induce superconductivity in the doped topological insulator Bi₂Se₃ by the proximity effect when it is sandwiched in a bilayer with an s-wave superconductor. For this we deposited bilayer thin films of Bi₂Se₃-NbN from which we prepared junctions of Bi₂Se₃-NbN-Au. Conductance spectra results of these junctions showed robust zero bias conductance peaks, which indicate unconventional superconductivity, but did not provide a conclusive evidence for MF. In the past year we investigated ultra-thin bilayers of Bi₂Se₃-NbN, and compared their properties to those of bare NbN reference films of the same thickness [4]. In my talk I shall discuss some of our recent results, in particular, gating effects of these bilayers, where significant magnetoresistance structures are observed also above the superconducting transition temperature.  

[1]  G. Koren, T. Kirzhner, E. Lahoud, K. B. Chashka, and A. Kanigel, Phys. Rev. B 84, 224521 (2011).                                                                                                                    

[2] G. Koren and T. Kirzhner, Phys. Rev. B 86, 144508 (2012). 

[3] Gad Koren, Tal Kirzhner, YoavKalcheim and Oded Millo, EPL 103, 67010, (2013).

[4] Gad Koren, Supercond. Sci. Technol. 28, 025003 (2015).