Regensburg 2004 – scientific programme

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TT: Tiefe Temperaturen

TT 17: Postersitzung II: Transport, Quantenkoh
ärenz, Quantenflüssigkeiten

TT 17.3: Poster

Tuesday, March 9, 2004, 14:30–19:00, Poster A

Green’s functions method for modelling the interplay between Coulomb blockade and Andreev reflection — •Ursula Schröter — FB Physik, Universität Konstanz, Universitätsstraße 10, 78457 Konstanz

We want to investigate charge transport across a superconducting island which is coupled to two superconducting reservoirs and whose potential is adjustable via a gate. In single-electron-transistor structures with weak coupling single electron tunneling is the dominant process and Coulomb blockade occurs. For superconducting materials multiple Andreev reflection (MAR) is also possible resulting in the transfer of several elementary charges in one process. With transmissions for the junctions no longer much smaller than one, as are found in mechanically controllable break junctions [1], these higher order processes give sub-gap contributions to the IV-characteristics. We regard two junctions in series, at least one of which has a fairly high transmission. The question is whether or not the MAR contribution to the current will be suppressed because of Coulomb blockade. Based upon an algorithm for a single junction [2] in a first ansatz we regard the two junctions as decoupled from one another but for the charging state of the island. A second ansatz shall include possible coherence over the entire structure. The two contacts are treated as two ’perturbations’ by folding Green’s functions into one another [3].

[1] E.Scheer et al., Nature 394, 154 (1998).

[2] J.C.Cuevas et al., Phys.Rev.B 54, 7366 (1996).

[3] U.Schröter, EPJ B 33, 297 (2003).