SUBGAP PEAK AND TOMASCH-MCMILLAN-ANDERSON OSCILLATIONS IN THE DENSITY OF STATES OF SNS BRIDGES

The quasiparticle spectra and the densities of states of superconducting-normal-superconducting junctions are computed from the WKBJ transformed Bogoliubov-de Gennes Equations (BdGE), which are solved by Picard iteration and numerical integration. It is shown that the influence of the proximity effect on the bound states can be modeled by a rectangular pair potential well of effective normal layer thickness 2a* = integral(-L)L [1 - DELTA(z)/DELTA]dz, where DELTA(z) is the pair potential of the junction, DELTA is its asymptotic constant value, and 2L is the total length of the sample. The density of states exhibits a subgap peak at energies less than DELTA besides the BCS peak at E = DELTA; for E > DELTA there are geometrical resonances which are due to electron-hole interferences in finite S layers of thickness L-a*.