Boundary Conditions in the Theory of Superconductivity

. In these Lecture Notes I discuss the boundary conditions for the quasiclassical Green's functions in the theory of superconductivity. I INTRODUCTION The quasiclassical Green's functions are a powerful method for investigating equilibrium and nonequilibrium superconductivity [1]. They can be used when the length scale a over which the macroscopic physical quantities of interest vary is much greater than the typical atomic scale F , the electron wavelength. In hybrid structures, due to the electron reflection occurring at the boundaries between different metals, macroscopic quantities do not vary slowly in the quasiclassical sense and the set of equations for the quasiclassical Green's functions needs to be complemented by appropriate boundary conditions that tell how to match the quasiclassical Green's functions on the different sides of a boundary once the scattering properties of the boundary are known. The derivation of such boundary conditions was done by Zaitsev [2] in a genera..