Microwave-induced steps in long homogeneous YBCO grain boundary junctions

We report on the dependence of zero-crossing microwave-induced Shapiro steps (SSn, n = 0, 1, 2,.) on applied power, magnetic field, and temperature in high quality YBa2Cu3O7 grain boundary Josephson junctions (GBJ). The microwave frequency (f(G) = 72.23 GHz) is adjusted so that it corresponds to f(G) = 1/4f(FS1), where f(FS1) is the frequency of the first Fiske resonance. The steps show a distinct asymmetry as function of the applied magnetic field and in certain regions of parameter space both SS+/-1 and SS+/-2 are crossing the zero bias current (I = 0) axis. Also half-harmonic generation and chaos-like structures are observed in the de IV curves.