Fractional Shapiro steps in a triangular single-plaquette Josephson-junction array

We study the dynamics of a triangular single-plaquette Josephson-junction array in the development of the fractional Shapiro steps. We show that synchronization on fractional steps can happen due to an intricate interplay of the three junctions as the plaquette is made dynamically unsymmetric, either by applying an external magnetic field or by changing the configuration of external currents. We propose a mechanism for synchronization when the asymmetry is only due to the frustration induced by the magnetic field.