Exact calculation of Shapiro step sizes for pulse-driven Josephson junctions

Abstract
A nonperturbative solution is presented for the current-voltage characteristics of Josephson junctions driven by square-wave and periodic δ-function signals. We find that no resonance conditions are required for the appearance of Shapiro steps–they appear for almost all amplitudes and frequencies of the driving pulse. Our calculations also permit a calculation of the boundaries of the Shapiro steps.