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TT: Tiefe Temperaturen

TT 8: Postersitzung I: Supraleitung

TT 8.53: Poster

Montag, 8. März 2004, 14:30–19:00, Poster A

Josephson coupling in Nb/Al₂O₃/Cu₁Ni_1−x/Nb tunnel junctions — •Martin Weides¹, Edward Goldobin², Reinhold Kleiner², and Hermann Kohlstedt¹ — ¹Institut für Festkörperforschung, Forschungszentrum Jülich, D-52425 Jülich — ²Physikalisches Institut-Experimentalphysik II, Universität Tübingen, D-72076 Tübingen

The realization of qubits for quantum computation attracts considerable interest. One of the approaches is to use π Josephson junctions (JJs) which can be realized as hybrids of superconducting (S) tunnel junction with a ferromagnetic inter-layer (F) on one side of the tunnel barrier (I), i.e. having SIFS structure. The magnetic film thickness determines the Josephson coupling and sets the phase coherence to either 0 or π.

SIFS multilayers consisting of Nb   (140 nm)/Al   (4)−Al₂O₃   (1)/CuNi   (0−30)/Nb   (40) were fabricated. The process parameters were derived from Josephson junctions with critical currents of about 0.1−1 kA   cm². The junction areas are ranged from 20.000 µ m² down to 10 µ m².

The first transport measurements of the junctions showed a monotonic decrease of I_cR_n for increasing FM-thickness. The generation of a semifluxon (cf. 1) pinned at the discontinuity of the magnetic layer thickness will be discussed. Since the semifluxon is a degenerated two state systems, it can be used as a qubit when the JJ is in the quantum limit.

[E. Goldobin et al., PRB 66, 100508 (2002)]