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TT: Tiefe Temperaturen
TT 1: Mesoskopische Systeme I
TT 1.7: Talk
Monday, March 24, 2003, 11:15–11:30, HSZ03
Doubling of the Poisson Noise in diffusive SIN junctions — •C. Hoffmann1, F. Lefloch1, D. Quirion1,2, and M. Sanquer1 — 1CEA-Grenoble, 17 rue des Martyrs, 38054 Grenoble, France — 2MPI für Festkörperforschung, 70569 Stuttgart, Germany
We studied the shot noise in superconductor (TiN) - strongly disordered normal metal (heavily doped Si) - junctions at temperatures down to 50 mK using a SQUID as fluctuations detector. The samples are described by SIN junctions where I stands for the Schottky barrier between TiN and silicon. At low energy eV<Ec (Ec is the Thouless energy) the shot noise has a slope of 4e, i.e. twice the Poisson noise (SP = 2eI), evidencing that coherent electron-hole pairs dominate in the current transport[1]. This is the direct confirmation that the enhancement of the conductance observed at low bias voltage[2] is due to coherent backscattering of quasiparticles towards the interface by the strong disorder in the silicon (reflectionless tunneling). When the excess of subgap conductance vanishes at finite voltage, the noise slope crosses over to the Poisson value 2e indicating a large quasiparticle contribution to the current at eV>Ec.
[1] F. Lefloch, C. Hoffmann, M. Sanquer, and D. Quirion, submitted to Phys. Rev. Lett.
[2] D. Quirion et al., J. Low Temp. Phys. 120, 361 (2000), Phys. Rev. B 65, 100508 (2002).