Quantum levels and quasi-local states of SINIS-structures

Quantum states of a superconductor-insulator-normal metal-insulator-superconductor sandwich (the SINIS-structure) are investigated in terms of the Bogoliubov-de Gennes equations. A dispersion equation for the quasi-particle spectrum at energies E < Δ (Δ is the energy gap in the superconductor) is obtained with taking into consideration the Andreev and the conventional electron scattering by the interfaces of the SINIS-structure. The spectrum allows one to calculate the Josephson current in the system. The transparency coefficient for the electrons of the continuous energy spectrum and the quasi-local states ('resonance levels') in the structure under consideration are calculated