Regensburg 2007 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 15: Superconductivity - Tunneling, Josephson Junctions, SQUIDs
TT 15.5: Vortrag
Dienstag, 27. März 2007, 15:00–15:15, H20
Josephson tunnel junctions with ferromagnetic barrier layer — •Martin Weides1, Hermann Kohlstedt1, Matthias Kemmler2, Dieter Koelle2, Reinhold Kleiner2, and Edward Goldobin2 — 1Institute for Solid State Research, Research Centre Jülich — 2Physikalisches Institut - Experimentalphysik II,
We have fabricated Nb/Al2O3/Ni0.6Cu0.4/Nb Josephson tunnel junctions[1]. Depending on the thickness of the ferromagnetic Ni0.6Cu0.4 layer and on the ambient temperature, the junctions were in the 0 or π coupled ground state[2]. The Al2O3 tunnel barrier allows to achieve rather low damping. The critical current density in the π state was up to 5 A/cm2 at T = 2.1 K, resulting in a Josephson penetration depth λJ as low as 160 µm. Experimentally determined junction parameters are well described by theory taking into account spin-flip scattering in the Ni0.6Cu0.4 layer and different interface transparencies. Using a ferromagnetic layer with a step-like thickness we obtain a 0–π junction with equal lengths and critical currents of 0 and π parts. The Ic(H) pattern shows a clear minimum in the vicinity of zero field. The ground state of our 330 µ m (1.3 λJ) long junction corresponds to a spontaneous vortex of supercurrent pinned at the 0–π phase boundary, carrying ∼ 6.7% of the magnetic flux quantum Φ0[3].
[1] Weides et al., Physica C 437-438, 349 (2006)
[2] Weides et al., Appl. Phys. Lett. 89, 122511 (2006)
[3] Weides et al., Phys. Rev. Lett. (12/2006)