Abstract
Superconductivity is a quantum state of matter characterized by the formation of Cooper pairs from time-reversal-symmetric electronic states. Mechanisms that break this symmetry, such as magnetic-impurity scattering and applied magnetic fields, are expected to be detrimental to superconductivity and suppress the critical temperature. Here, we report the observation of pronounced increases in the mean-field critical temperature on application of a parallel magnetic field in two different two-dimensional superconducting systems: ultrathin, homogeneously disordered amorphous Pb films and the two-dimensional electron gas at the interface of LaAlO3 and SrTiO3. In the amorphous Pb films, the critical-temperature increases exhibit a systematic dependence on the film thickness. Significantly, the presence of paramagnetic impurities in the films diminishes the effect of field enhancement of superconductivity. These observations mark a radical departure from the current understanding of the interactions between magnetic fields and superconductivity.
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Acknowledgements
The authors would like to thank S. Paetel and C. Richter for their help in processing the LaAlO3/SrTiO3 samples, and acknowledge discussions with R. C. Dynes, Y. Dubi, L. P. Gor’kov, J. Mannhart, P. Schlottmann and S. von Molnár. O.V. was supported in part by a National Science Foundation CAREER award under grant no DMR-0955561.
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H.J.G., A.K. and L.Y. made the measurements on the a-Pb films. H.J.G. and L.Y. made the measurements on the LaAlO3/SrTiO3 sample. M.P.W. and D.G.S. prepared the LaAlO3/SrTiO3 sample. L.W. and O.V. provided theoretical guidance. P.X. and H.J.G. prepared the manuscript and all authors commented on the manuscript. P.X. supervised the project.
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Jeffrey Gardner, H., Kumar, A., Yu, L. et al. Enhancement of superconductivity by a parallel magnetic field in two-dimensional superconductors. Nature Phys 7, 895–900 (2011). https://doi.org/10.1038/nphys2075
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DOI: https://doi.org/10.1038/nphys2075
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