Abstract
Single-layer FeSe film on SrTiO3(001) has recently come to the fore as an interfacial superconducting system, with a transition temperature that is significantly enhanced with respect to bulk FeSe. The mechanism for this enhancement, and indeed for the superconductivity itself, is therefore of great interest. Although the film has a simple Fermi surface topology, its pairing symmetry is unclear. By using low-temperature scanning tunnelling microscopy, we have systematically investigated the superconductivity of single-layer FeSe/SrTiO3 films, and report a fully gapped tunnelling spectrum and magnetic vortex lattice in the film. Quasi-particle interference patterns reveal scatterings between and within the electron pockets, and put constraints on possible pairing symmetries. By introducing impurity atoms onto the sample, we show that magnetic impurities such as Cr and Mn can locally suppress the superconductivity, but non-magnetic impurities (Zn, Ag and K) do not. Our results indicate that single-layer FeSe/SrTiO3 has a plain s-wave pairing symmetry, with an order parameter that has the same phase on all Fermi surface sections.
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Acknowledgements
We thank X.-G. Gong and D.-H. Lee for useful discussions. This work is supported by the National Science Foundation of China, and National Basic Research Program of China (973 Program) under the grant No. 2012CB921402, No. 2011CBA00112, and No. 2011CB921802.
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The sample growth and STM measurements were performed by Q.F., W.H.Z. and T.Z. The data analysis was performed by Q.F., X.L., J.P.H., T.Z. and D.L.F. T.Z. and D.L.F. coordinated the whole work and wrote the manuscript. All authors have discussed the results and the interpretation.
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Fan, Q., Zhang, W., Liu, X. et al. Plain s-wave superconductivity in single-layer FeSe on SrTiO3 probed by scanning tunnelling microscopy. Nature Phys 11, 946–952 (2015). https://doi.org/10.1038/nphys3450
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DOI: https://doi.org/10.1038/nphys3450
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