We report on measurements of the ac Josephson effect in three-dimensional topological insulator (TI) Josephson junctions with Fermi energy tuning using a back gate. We successfully tune the Fermi energy into the bulk gap of the TI. We observe that the Josephson energy as a function of the gate voltage has a dip feature, indicating the presence of specular Andreev reflections. We study the ac Josephson effect with detection of both Shapiro steps and Josephson emission. The obtained results show no signature of Majorana modes. With the support of simulations, we conclude that the observation of the fractional ac Josephson effect may be complicated by both a large parallel capacitance and a small ratio of current carried in 4π period modes compared to conventional 2π modes.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics