Fractional Josephson Effect in Topological Insulator Nanoribbons

• Speaker: Doh, Yong-Joo (Department of Physics and Photon Science, Gwangju Institute of Science and Technology, Korea)
• Co-authors: Kim, Hong-Seok (GIST), Kim, Nam-Hee (GIST), Jang, Yeong-Min (GIST), Hou, Yasen (UC Davis, USA), Yu, Dong (UC Davis, USA)

Topological insulator (TI) nanowire combined with conventional s-wave superconductor is expected to provide the topological superconducting state for hosting the Majorana fermion, which is essential for the topological quantum computation. Here, we report the experimental evidences of the topological supercurrent through surface states in (Bi0.81Sb0.19)2Se3 TI nanowire-PbIn superconductor Josephson junctions. When an axial magnetic filed is applied, the Josephson supercurrent oscillates, and their period is consistent with the Aharonov-Bohm (AB) oscillations of normal conductance, indicate that the supercurrent is caused by the topological surface states. Furthermore, when we applied microwaves to the junctions, anomalous Shapiro steps with the first step missing are observed at around 300 mK. In the topological superconducting state, the supercurrent has a 4-period and is expected to show doubled Shapiro steps, so called the factional Josephson effect. Therefore, our anomalous Shapiro steps can be caused from the topological supercurrent, and it is also verified by numerical calculations. To the best of our knowledge, our experimental results are for the first time in the world to simultaneously demonstrate the surface supercurrent AB oscillations and fractional Josephson effect in a topological nanowire.