Shapiro steps in InAs-based Josephson junctions with epitaxial Al contacts*

Semiconductor-based Josephson junction provide a platform to study the proximity effect and can serve as a platform for the realization of in topological superconductivity. Recently our group has demonstrated the possibility to have a highly transparent contact between the superconductor and the semiconductor by combining InAs high mobility surface 2D-dimensional electron gases with epitaxially grown aluminium.
The interplay between the induced superconducting gap and the spin-orbit coupling in those structure is still an on-going field of research. While DC measurements can allow to access the current-phase relation of those structure, some details could be masked by relaxation processes. We utilize microwave radiation on Josephson junctions to unmask the periodicity of the current phase relation. We study Shapiro steps that appear in the IV characteristic of a junction under microwave irradiation. We observe a missing first Shapiro step below 6 GHz that may point to a 4π component in the current-phase relation of those junctions. Similar signatures have been observed in HgTe (in the topological regime) but given the high transparency of our contacts they may arise from Landau-Zener transitions in our InAs structures.