AC Josephson effect in a capacitively shunted graphene Josephson junction

The AC Josephson effect is being used to detect signatures of novel modes in Josephson junctions. However, complex behavior of these junctions under RF radiation can also from trivial effects, like the presence of a large shunting capacitance. Here we study the AC Josephson effect on a junction made of graphene encapsulated in boron nitride and contacted by electrodes made of a superconducting molybdenum-rhenium alloy. In regions where chemical potential is close to the charge-neutrality point and the RF drive current is comparable with critical current, this device demonstrated a bi-stability between the first Shapiro steps, indicating the Josephson junction is in a chaotic regime. A full description of the chaotic physics observed is presented. These observations cast doubt over arguments that AC Josephson effect in the low RF drive amplitude region would offer the opportunity to observe 4-π current phase relation in topological Josephson junctions.