Shapiro Steps and Negative Absolute Resistance in Microwave-Driven Shunted Josephson Junctions

Topological Josephson junctions (JJs) have been studied as promising candidates to host Majorana fermions, especially because the phase across the junction can be used to tune the topological phase. When a microwave drive is applied to a JJ, it is expected to observe integer and possibly fractional constant voltage steps, Shapiro steps, appearing in the Voltage-Current characteristic due to phase locking. In this work, we observe and study these dynamics in 100nm JJs fabricated on InAs surface quantum wells coupled to epitaxial Al contacts in relation to the applied microwave bias amplitude and frequency as well as an applied external magnetic field. When such nonlinear systems are driven out of equilibrium, exotic behavior such as negative absolute resistance (NAR) could possibly arise that have promising applications in electronics and quantum computing, mainly qubit state manipulation and readout. We discuss these observations in presence of an in-plane magnetic field.