Shot noise in hybrid normal and superconducting multilayers

n coherent conducting multilayers with junction transparencies D comparable to unity, quantum fluc- tuations, which follow from the probabilistic nature of the backscattering restricted by the Pauli prin- ciple, are reduced in comparison to the standard Schottky result. Voltage dependence of the low- temperature shot noise is calculated for hybrid normal-superconductor heterostructures with ultra-thin insulating barriers, where the transparency distribution is a bimodal function with two peaks at D = 0 and D = 1, and the difference between s- and d-wave superconductors is emphasized. The theoretical results are compared with our experimental shot-noise data for Nb/Al-AlOx-Nb junctions. To improve the signal to noise ratio of the measurement system the junctions dimensions have been reduced below 1 μm2 and measurement temperature below 2 K has been used. We have also studied double- barrier N1-I1-N2-I2-S structures as a model system for the transition from quantum (coherent) to classical (incoherent) regime of the charge transport and analyzed the impact of inelastic scatterings in the N2 interlayer on its shot-noise characteristics.