PELTIER EFFECT IN NORMAL-METAL-SUPERCONDUCTOR 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 similar or equal to 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 how out of the normal metal. In clean contacts, the optimum transparency is about 0.1 at T=0.3 Delta and decreases with temperature roughy 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)/IR(T) similar or equal to 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).