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Plain s-wave superconductivity in single-layer FeSe on SrTiO3 probed by scanning tunnelling microscopy

Nature Physics volume 11, pages 946–952 (2015)Cite this article

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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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Figure 1: Surface topography and superconducting gap spectrum of single-layer FeSe/SrTiO3(001).
Figure 2: Magnetic vortex states of single-layer FeSe/SrTiO3(001).
Figure 3: QPI mappings of single-layer FeSe/SrTiO3(001).
Figure 4: QPI intensity analysis for different scattering channels.
Figure 5: In-gap states induced by magnetic impurities Cr and Mn.
Figure 6: Absence of the in-gap states on non-magnetic impurities (Zn, Ag and K).

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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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Authors and Affiliations

  1. Department of Physics, State Key Laboratory of Surface Physics, and Advanced Materials Laboratory, Fudan University, Shanghai 200433, China

    Q. Fan, W. H. Zhang, X. Liu, Y. J. Yan, M. Q. Ren, R. Peng, H. C. Xu, B. P. Xie, T. Zhang & D. L. Feng

  2. Collaborative Innovation Center of Advanced Microstructures, Fudan University, Shanghai 200433, China

    B. P. Xie, T. Zhang & D. L. Feng

  3. Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100080, China

    J. P. Hu

  4. Department of Physics, Purdue University, West Lafayette, Indiana 47907, USA

    J. P. Hu

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Contributions

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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Correspondence to T. Zhang or D. L. Feng.

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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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