Introduction to inhomogeneous superconductors

After a brief historical perspective on the motivation for study of inhomogeneous superconductors, the formulation of Ginzburg‐Landau equations suitable for such systems is reviewed. Attention is given to the important role of boundary conditions on ψ and h/ψ at interfaces and to the connection with Josephson effect coupling between discrete elements, as in layered compounds and granular superconductors. Finally, the resistive properties of composite wire containing finite length superconducting filaments in a normal metal matrix are discussed in more detail, with emphasis on proximity effect coupling and on the critical behavior of resistance and maximum supercurrent near the percolation threshold.