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0-pi Josephson tunnel junctions with ferromagnetic barrier

M. Weides, M. Kemmler, E. Goldobin, H. Kohlstedt, R. Waser, D. Koelle, R. Kleiner

cond-mat.supr-conarXiv:cond-mat/0605656

Abstract

We fabricated high quality Nb/Al2O3/Ni0.6Cu0.4/Nb superconductor-insulator-ferromagnet-superconductor Josephson tunnel junctions. Using a ferromagnetic layer with a step-like thickness, we obtain a 0-pi junction, with equal lengths and critical currents of 0 and pi parts. The ground state of our 330 microns (1.3 lambdaJ) long junction corresponds to a spontaneous vortex of supercurrent pinned at the 0-pi step and carrying ~6.7% of the magnetic flux quantum Phi0. The dependence of the critical current on the applied magnetic field shows a clear minimum in the vicinity of zero field.

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