•Harald Kloos und Andrei Zaikin

Forschungszentrum Karlsruhe, Institut für Nanotechnologie, 76021
Karlsruhe, Germany

A normal metal layer in good electric contact to a superconductor exhibits
properties sumarized under the term proximity effect, i.e. Andreev reflection
and the formation of a gap in the density of states which is much smaller
than the superconducting order parameter D.
At low temperatures thermodynamic properties of small isolated superconducting
grains depend on the parity of the number of electrons they carry, because
pairs of electrons can form Cooper pairs and enter the condensate, whereas
the lowest available state for an unpaired electron is given by D.
We investigate the parity effect in an SN layer structure within the quasiclassical
Green's functions formalism for arbitrary concentrations of nonmagnetic
impurities. The temperature T^{*} is estimated, below which parity
effects dominate the physical properties of the sample due to the proximity
induced features of the N-layer. It is shown that the free energy difference
between ensembles with even and odd numbers of particles at zero temperature
coincides with the proximity gap of the normal metal layer. At finite temperatures
the entropy factor is related to the density of states of the sample.