Shapiro Steps Induced by Resonance Irradiation

We consider a Josephson junction coupled to a high-quality parallel resonance circuit under microwave irradiation on the resonance frequency. The phase locking of Josephson oscillations, manifesting itself through Shapiro steps, is studied using an analytical theory developed for the circuit. Substantial change in the amplitude of the oscillating component of the Josephson phase within the phase-locking range determines specificity of the step behavior. This analysis is compared with the results of a numerical simulation.