Experimental Studies of Mode-Locking and Circle Maps in Inductively Shunted Josephson Junctions

The nonlinear dynamical behaviour of a Josephson tunnel junction shunted by a large inductivity is investigated experimentally. The system exhibits spontaneous oscillations in the voltage signal when biased with a constant current. We observe mode-locking and quasi-periodicity if an a.c.-current is added to the bias. Return maps are constructed from the measured time signal, showing that the dynamical behaviour can be described in terms of a 1D circle map. Numerical calculations reproduce and extend the experimental results.