Current noise effects on the microwave induced steps in current fed Josephson junctions

Harmonic and subharmonic microwave induced steps in the I-V characteristics of current fed Josephson junction were found and investigated by numerical and approximate analytical methods, for a purely sinusoidal Josephson current. The dependence of the steps on the various parameters is given and their local stability is discussed. Various types of I-V characteristics are shown. We have introduced thermal noise effects via a Langevin term in the equation of motion. The smaller steps are easily washed out by the thermal noise. The width of the fundamental step was found to be proportional to T^xfor the range of parameters which we used, wherex \gsim 1/2.