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Experimental Evidence of a φ Josephson Junction


  Hanna Sickinger [1]  ,  Adi Lipman [2]  ,  Martin Weides [3]  ,  Roman G. Mints [2]  ,  Hermann Kohlstedt[4]  ,  Dieter Koelle [1]  ,  Reinhold Kleiner [1]  ,  Edward Goldobin [1]  
 [1] Physikalisches Institut and Center for Collective Quantum Phenomena in LISA, Universität Tübingen, Auf der Morgenstelle 14, D-72076 Tübingen, Germany
[2] The Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel
[3] Peter Grünberg Institute and JARA-Fundamentals of Future Information Technology, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
[4] Nanoelektronik, Technische Fakultät, Christian-Albrechts-Universität zu Kiel, D-24143 Kiel, Germany

We demonstrate experimentally the existence of Josephson junctions having a doubly degenerate ground state with an average Josephson phase ψ=±φ. The value of φ can be chosen by design in the interval 0<φ<π. The junctions used in our experiments are fabricated as 0-π Josephson junctions of moderate normalized length with asymmetric 0 and π regions. We show that (a) these φ Josephson junctions have two critical currents, corresponding to the escape of the phase ψ from -φ and +φ states, (b) the phase ψ can be set to a particular state by tuning an external magnetic field or (c) by using a proper bias current sweep sequence. The experimental observations are in agreement with previous theoretical predictions.