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Reversing the direction of the supercurrent in a controllable Josephson junction

Nature volume 397, pages 43–45 (1999)Cite this article

Abstract

When two superconductors are connected by a weak link, a supercurrent flows, the magnitude of which is determined by the difference in the macroscopic quantum phases of the superconductors. This phenomenon was discovered by Josephson1 for the case of a weak link formed by a thin tunnel barrier: the supercurrent, I, is related to the phase difference, π, through the Josephson current–phase relation, I = Icsinπ, with Ic being the critical current which depends on the properties of the weak link. A similar relation holds for weak links consisting of a normal metal, a semiconductor or a constriction2. In all cases, the phase difference is zero when no supercurrent flows through the junction, and increases monotonically with increasing supercurrent until the critical current is reached. Here we use nanolithography techniques to fabricate a Josephson junction with a normal-metal weak link in which we have direct access to the microscopic current-carrying electronic states inside the link. We find that the fundamental Josephson relation can be changed from I = Icsinπ to I = Icsin(π + π)—that is, a π-junction—by controlling the energy distribution of the current-carrying states in the normal metal. This fundamental change in the way these Josephson junctions behave has potential implications for their use in superconducting electronics as well as in (quantum) logic circuits based on superconductors.

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Figure 1: Electronic distribution function and the sample layout.
Figure 2: Critical current of the SNS junction as a function of the control voltage.
Figure 3: VSNS, the voltage across the junction, and the resistance of the control channel as a function of the current I.

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Acknowledgements

We thank F. K. Wilhelm for discussions. This work was supported by the Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO) through the Stichting voor Fundamenteel Onderzoek der Materie (FOM).

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Author notes

  1. A. F. Morpurgo

    Present address: Department of Physics, Stanford University, Stanford, California, 94305-4060, USA

Authors and Affiliations

  1. Department of Applied Physics and Material Science Center, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, The Netherlands

    J. J. A. Baselmans, A. F. Morpurgo, B. J. van Wees & T. M. Klapwijk

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  1. J. J. A. Baselmans
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  2. A. F. Morpurgo
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  3. B. J. van Wees
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  4. T. M. Klapwijk
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Correspondence to J. J. A. Baselmans.

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Baselmans, J., Morpurgo, A., van Wees, B. et al. Reversing the direction of the supercurrent in a controllable Josephson junction. Nature 397, 43–45 (1999). https://doi.org/10.1038/16204

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