A novel phase-locked state in discrete Josephson oscillators

We have measured a novel phase-locked state in discrete parallel arrays of Josephson junctions which can be used for oscillator applications. Previous Josephson junction oscillators have been based on the Eck step, where a large-amplitude wave of nearly a single harmonic travels through the system. Multi-row systems biased on the Eck step could improve the output power, but their in-phase oscillations are difficult to stabilize. A new in-phase state which is very stable has been measured as a step in the dc I-V characteristic of one and two row systems. Simulations show that large-amplitude oscillations of two harmonics characterize the state. The rows are phase-locked and in-phase for the higher harmonic. We present an analytic expression for the oscillation frequencies and their magnetic tunability.