Search for Majorana Fermions on Bi2Se3 and Cu0.2Bi2Se3 Using 4K & mK-STM with W or Nb Tips

The search for Majorana Fermions in condense matter physics has been getting a lot of attention in the last few years. Different theoretical proposals suggested experimental setups to identify these states (for a review see [1, 2]). Many relied on finding a zero-bias conductance peak (ZBCP) in topological insulator - superconductor heterostructures, with and without the application of a magnetic field. At LPS we were using a homemade 4K and mK-STM [3] to look at the topological insulator Bi2Se3 and the topological superconductor Cu0.2Bi2Se3 using both normal W and superconducting Nb tips [4]. Our results include data from all four possible junctions. In this talk I will be discussing; gap and sub-gap features arising when Nb islands are grown on Bi2Se3, proximity induced superconductivity on the surface of Bi2Se3 with Nb tip, varying superconducting gaps on Cu0.2Bi2Se3 and sub-gap states/ZBCP on the surface of Cu0.2Bi2Se3 due to variations in the magnetic field (possible vortexes). The SIS junctions display super-current peaks that are not bound to zero bias. Instead, they decay away from zero with extra peaks at finite voltage. I will explain this behavior by Cooper-pair current through ultra-small Josephson junctions and loss of energy to modes of the environment, both predicted by the P (E) theory [5]. To conclude, I will show microwave response of super-current in Nb-Nb junction and suggest its possible application in my search for Majorana fermions.

For further information please contact Joe Stroscio, 301-975-3716, joseph.stroscio [at] nist.gov (joseph[dot]stroscio[at]nist[dot]gov)