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TT: Tiefe Temperaturen

TT 1: Supraleitung in mesoskopischen und nanoskopischen Strukturen

TT 1.4: Hauptvortrag

Montag, 22. März 1999, 11:15–11:45, F2

Tunable supercurrent in superconductor-normal metal-superconductor Josephson-junctions — •T. M. Klapwijk, A. Mopurgo, and B.J. van Wees — Department of Applied Physics and Materials Science Center, University of Groningen, The Netherlands

The supercurrent in a Josephson junction is carried by phase-dependent states, which may have a positive or negative direction. The net supercurrent depends on the occupation of those states. A thermal distribution leads always to a supercurrent which runs in the direction of the phase-gradient or phase-difference. A two-step distribution-function as realized in short mesoscopic normal wires leads to a possible reversal of the direction of the supercurrent, rendering it into a so-called pi-state, with the lowest energy state being a phase-difference of pi. This effect, anticipated theoretically by Volkov [1], Yip [2] and Wilhelm et al. [3], has been observed recently in mesoscopic devices using niobium-gold-niobium Josephson junctions in which the occupation of states in the gold can be controlled externally.

[1] A. F. Volkov, Phys. Rev. Lett. 74, 4730 (1995).

[2] S.-K. Yip, Phys. Rev. B, 58, 5803 (1998).

[3] F. K. Wilhelm, G. Schön, and Andrei. D. Zaikin, Phys. Rev. Lett. 81, 1682 (1998).