Size effects in the density of states in normal-metal-superconductor and superconductor-normal-metal-superconductor junctions.

The quasiparticle local density of states ~LDOS! is studied in clean normal-metal–superconductor ~NS! and superconductor–normal-metal–superconductor ~SNS! junctions with increasing transverse size, from quasione-dimensional to three-dimensional. It is shown that finite transverse dimensions are related to pronounced effects in the LDOS, such as fast oscillations superimposed on the quasiparticle interference oscillations ~for NS! and additional peaks in the bound state spectrum in the subgap region ~for SNS!. Also, the validity of the Andreev approximation is discussed. It turns out to be an acceptable approximation in all situations tested. @S0163-1829~96!07430-9#