Quasiperiodically driven Josephson junctions: strange nonchaotic attractors, symmetries and transport

We consider the dynamics of the overdamped Josephson junction under the influence of an external quasiperiodic driving field. In dependence on parameter values either a quasiperiodic motion or a strange nochaotic attractor (SNA) can be observed. The latter corresponds to a resistive state in the current-voltage characteristics while for quasiperiodic motion a finite superconducting current exists for zero voltage. It is shown that in the case of SNA a nonzero mean voltage across the junction can appear due to symmetry breakings. Based on this observation a detailed symmetry consideration of the generalized equation of motion is performed and symmetry conditions ensuring zero mean voltage across the junction are found.