ИСТИНА

We studied Shapiro steps induced by rf current applied to an underdamped Josephson junction at resonance frequency, when the resonance is provided by the in parallel connected junction capacitance and external LC circuit. As far as the resonance excitation of the pulse component of Josephson phase yields from both the force impact of the rf current and impact of Josephson oscillation process including parametric mechanism as well, their competition determines specific character of the phase-locking manifestation. In particular, this competition is responsible for substantial change in amplitude of the pulse component within Shapiro step and hence asymmetric position of the step in IV curve of the junction. Analytic theory is developed and compared with results of numerical simulation.