Abstract
The d.c. Josephson effect refers to the dissipationless electrical current—the supercurrent—that can be sustained across a weak link connecting two bulk superconductors. This effect probes the nature of the superconducting state, which depends crucially on spatial dimensionality. For bulk (that is, three-dimensional) superconductors, the superconductivity is most robust and the Josephson effect is sustained even at non-zero temperature. However, in wires and thin films, thermal and quantum fluctuations play a crucial role. In superconducting wires, these effects qualitatively modify the electrical transport across a weak link. Despite several experiments involving weak links between thin-film superconductors, little theoretical attention has been paid to the electrical conduction in such systems. Here, we analyse the case of two superconducting thin films connected by a point contact. Remarkably, the Josephson effect is absent at non-zero temperature. The point-contact resistance is non-zero and varies with temperature in a nearly activated fashion, with a universal energy barrier set by the superfluid stiffness characterizing the films. This behaviour reflects the subtle nature of thin-film superconductors and should be observable in future experiments.
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Acknowledgements
We gratefully acknowledge discussions with L. Balents, A. Bezryadin, A. Paramekanti and X.-G. Wen. This research is funded by the US Department of Defense NDSEG program (M.H.), the US National Science Foundation (G.R. and M.P.A.F.) and the US Department of Energy, Division of Material Sciences (through the Frederick Seitz Materials Research Laboratory at UIUC) (P.G.).
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Hermele, M., Refael, G., Fisher, M. et al. Fate of the Josephson effect in thin-film superconductors. Nature Phys 1, 117–121 (2005). https://doi.org/10.1038/nphys154
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DOI: https://doi.org/10.1038/nphys154
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