QUASI-PARTICLES ON A NORMAL SPHERE IN A SUPERCONDUCTING CONTINUUM

In N/S point contacts with ''high energy'' quasiparticle injection all owing for phonon production, a non-equilibrium situation is produced w hich may be described as a normal bubble within the superconducting ha lf-space. This non-equilibrium state leads to a number of interesting features in the current-voltage characteristics such as hysteretic jum ps and oscillations in the excess current. The latter have been interp reted as geometrical resonances due to interferences of bound quasipar ticles in the normal bubble. As a first approach to this complex situa tion we investigate the quasiparticle spectrum of a normal sphere. The density of the bound states possesses a finite gap at an energy E(G) < Delta, and subgap peaks due to a cut-off in each subband of the boun d states spectrum. Finally, we calculate the total energy as a functio n of the normal sphere radius R. It contains periodic contributions, c aused by the periodic entering of new bound state subbands which split off the continuum E > Delta and enter the gap regime E < Delta. These periodic contributions are tentatively discussed in context with the above-mentioned experimentally observed oscillations in the excess cur rent.