PELTIER EFFECT IN NS MICROCONTACTS

We have calculated the heat current in the normal metal/insulator/ superconductor contacts with arbitrary transparency of the insulator barrier. In the tunneling limit (small transparencies), the heat flow out of the normal metal reaches its maximum at temperature $T\simeq 0.3\Delta$. At higher values of transparency, the interplay between single-particle tunneling and Andreev reflection determines optimum transparency which maximizes the density of heat flow out of the normal metal. In clean contacts, the optimum transparency is about $0.1$ at $T=0.3\Delta$ and decreases with temperature roughly as $(T/\Delta)^{3/2}$. In disordered contacts, disorder enhances Andreev reflection and shifts the optimum point towards smaller transparencies. The optimal ratio of the barrier resistance to the resistance of the normal electrode is $R_N/R_T \simeq 0.01$ at $T=0.3 \Delta$ and decreases with temperature similarly to clean contacts. For disordered contacts we also plot current-voltage characteristics for arbitrary values of the ratio $R_N/R_T$.