The
Josephson effect is the phenomenon of
supercurrent—i.e. a current that flows indefinitely long without any voltage applied—across a device known as a
Josephson junction (JJ), which consists of two
superconductors coupled by a weak link. The weak link can consist of a thin insulating barrier (known as a
superconductor–insulator–superconductor junction, or S-I-S), a short section of non-superconducting metal (S-N-S), or a physical constriction that weakens the superconductivity at the point of contact (S-s-S).