Long Josephson junction

In superconductivity, a long Josephson junction (LJJ) is a Josephson junction which has one or more dimensions longer than the Josephson penetration depth ${\displaystyle \lambda _{J}}$. This definition is not strict.

In terms of underlying model a short Josephson junction is characterized by the Josephson phase ${\displaystyle \phi (t)}$, which is only a function of time, but not of coordinates i.e. the Josephson junction is assumed to be point-like in space. In contrast, in a long Josephson junction the Josephson phase can be a function of one or two spatial coordinates, i.e., ${\displaystyle \phi (x,t)}$ or ${\displaystyle \phi (x,y,t)}$.