Energy storage and subharmonic oscillations in Josephson junctions

The energy stored in the magnetic and electric field near a superconducting point contact is typically the same magnitude as the coupling energy which produces the Josephson effect in the weakly coupled superconductors. These energies are usually of order one electron volt. One consequence of energy storage in both the electric and magnetic field is that the junction can oscillate at a fundamental frequency ω=2eV/hn, where n is an integer. The dynamics of these subharmonic oscillations have been studied for a model in which the magnetic and electric energies are represented as being stored in an inductance and a capacitance respectively. The model was studied numerically for various biasing conditions, and the behavior compared to experimental data. A simple analytic approximation was developed that gives physical insight into the mechanism that creates the subharmonic oscillations. By use of an electrical analog model, we demonstrated that these subharmonic oscillations can phase lock with an externally applied signal.