RF-induced steps in mutually coupled, two-dimensional distributed Josephson tunnel junctions

The amplitudes of the current steps in the I-V characteristics of mutually coupled two-dimensional distributed Josephson tunnel junctions driven by microwaves are investigated. For this purpose a numerical computation algorithm that is based on a planar resonator model for the individual Josephson tunnel junctions is used to calculate the DC current density distribution. In addition to the fundamental microwave frequency, harmonic contents of the tunneling current are also considered. The lateral dimensions of the individual junctions are small compared to the microwave wavelength and the Josephson penetration depth, giving an almost constant current density distribution. Therefore, the coupled junctions can give much greater step amplitudes than a single junction with an equal tunneling area, because of their nonuniform current density distribution. The calculation show a strong dependence of the Shapiro step amplitudes with respect to the coupling of the tunnel junctions. These studies imply that the choice of proper coupling conditions is important to achieve maximum step amplitudes. These results are helpful in designing tunnel junctions with optimized step amplitudes.