Superconducting critical currents for thick, clean superconductor—normal-metal—superconductor junctions

Superconducting critical currents have been studied for superconductor—normal-metal—superconductor ($S-N-S$) junctions as a function of temperature, magnetic field, and thickness in order to determine the spatial variation of the superconducting pair potential in the normal-metal region. Emphasis is placed on the thick, clean limit for the normal metal. The temperature dependence of $J_c$ obeys predictions based on the de Gennes-Werthamer theory, and the magnitude of $J_c$ is reasonable. In a high magnetic field, $J_c$ falls exponentially with increasing magnetic field, indicating that the inverse of the decay length of the order parameter, $K_N^{-1\mathrm{}}$, is approximately linear in $H$.