Noise properties of d-wave superconducting junctions

We have experimentally investigated the noise in a normal metal-d-wave supe rconductor (NS) junction with a {110} and {100} oriented interfaces at 65 k Hz frequency, where the noise power spectrum is white. The NS junctions are silver-nature barrier-YBa2Cu3Oy epitaxial thin films in planar junction ge ometry. Both the {110} and {100} films show zero bias conductance peak (ZBC P). For low conductance junction, the observed noise power spectrum is smal l at low bias and rises rapidly at high bias. The observed shot noise is qu alitatively different from that in a normal metal-s-wave superconductor. Th e measured noise of high conductance NS junction is significantly larger th an that of low conductivity junction. We attribute this enhanced shot noise to the occurrence of multiple Andreev reflection in the nature barrier.