Cooper-pair charge solitons: The electrodynamics of localized charge in a superconductor

One-dimensional arrays of small-capacitance Josephson junctions exhibit a current-voltage curve that is characterized by a zero-current state for bias voltage below a threshold voltage $V_t$. The threshold voltages can be modulated with an external magnetic field $B$, which tunes effective Josephson coupling between adjacent electrodes of the array. The dependence of $V_t$ on $B$ is well explained by a model where $V_t$ is the injection voltage for a Cooper-pair charge soliton.