Berlin 2012 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 7: Transport and Diffusion II
MM 7.5: Vortrag
Montag, 26. März 2012, 12:30–12:45, H 1029
Critical current noise in rough Josephson junctions — •Pierre-Luc Dallaire-Demers1, Mohammad Ansari2, and Frank Wilhelm-Mauch1 — 1Universität des Saarlandes, Saarbrücken, Deutschland — 2University of Waterloo, Waterloo, Canada
While dissipationless, Josephson junctions as elements in superconducting nanocircuits are plagued by intrinsic noise mechanisms that will limit the coherence time of future high-precision quantum devices. Significant sources of current fluctuations may be caused by the non-cristallinity and disorder of the oxide layer separating the two superconducting leads. A microscopic calculation of the spectral density of noise of a rough superconducting tunnel junction is presented in this work. To account for disorder, a Josephson junction is modelled as a set of pinholes with a universal bimodal distribution of transmission eigenvalues that add their noise power incoherently. Each pinhole is treated as a ballistic point contact with an intrinsic thin barrier that modulates the transmission coefficient. The noise spectrum is computed using the quasiclassical Green's function method for non-equilibrium superconductivity. This formalism allows us to investigate high and low transmission limits at finite temperature for any relevant frequency. As suggested by experiments, low transmission pinholes generate shot noise while fast switching between the subgap states of high transmission channels create a strong non-poissonian low-frequency noise yet to be measured. The fluctuation of the low-frequency noise from one sample to the other is also found to be significant when the phase of the order-parameter is anti-symmetric across the junction.