Superconductivity in multiple interface geometry: Applicability of quasiclassical theory

The method of two-point quasiclassical Green's function is reviewed and its applicability for description of multiple reflections/transmissions in layered structures is discussed. The Green's function of a sandwich built of super-conducting layers with a semi-transparent interface is found with the help of recently suggested quasiclassical method [A. Shelankov and M. Ozana, Phys. Rev. B 61. 7077 (2000)], as well as exactly, from thc Gor'kov equation. By the comparison of the results of the two approaches, thc validity of the quasiclassical method for thc description of real (non-integrable) systems is confirmed.