Atomic line defects and zero-energy end states in monolayer Fe(Te,Se) high-temperature superconductors

Abstract

Majorana zero-energy bound states have been proposed to exist at the ends of one-dimensional Rashba nanowires proximity-coupled to an s-wave superconductor in an external magnetic field1,2. Such hybrid structures are a central platform in the search for non-Abelian Majorana zero modes that may be applied in fault-tolerant topological quantum computing3,4. Here we report the discovery of zero-energy bound states simultaneously appearing at both ends of a one-dimensional atomic line defect in monolayer iron-based high-temperature superconductor FeTe0.5Se0.5 films. The spectroscopic properties of the zero-energy bound states, including the temperature and tunnelling barrier dependences, as well as their fusion induced by coupling on line defects of different lengths are found to be robust and consistent with those of the Majorana zero modes. These observations suggest a realization of topological Shockley defects at the ends of an atomic line defect in a two-dimensional s-wave superconductor that can host a Kramers pair of Majorana zero modes protected by time-reversal symmetry along the chain. Our findings reveal a class of topological line defect excitations in two-dimensional superconductor FeTe0.5Se0.5 monolayer films and offer an advantageous platform for generating topological zero-energy excitations at higher operating temperatures, in a single material, and under zero external magnetic field.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Fig. 1: STM topography and double-gap superconductivity of 1-UC FeTe0.5Se0.5/STO.
Fig. 2: ZEBSs at the ends of a long atomic line defect in 1-UC FeTe0.5Se0.5/STO.
Fig. 3: ZEBSs at the ends of a short atomic line defect in 1-UC FeTe0.5Se0.5/STO.

Data availability

The data represented in Figs. 13 are available as source data. All other data that support the plots within this paper are available from the corresponding author upon reasonable request.

References

  1. 1.

    Lutchyn, R. M., Sau, J. D. & Das Sarma, S. Majorana fermions and a topological phase transition in semiconductor–superconductor heterostructures. Phys. Rev. Lett. 105, 077001 (2010).

    ADS  Article  Google Scholar 

  2. 2.

    Oreg, Y., Refael, G. & von Oppen, F. Helical liquids and Majorana bound states in quantum wires. Phys. Rev. Lett. 105, 177002 (2010).

    ADS  Article  Google Scholar 

  3. 3.

    Alicea, J., Oreg, Y., Refael, G., von Oppen, F. & Fisher, M. P. A. Non-Abelian statistics and topological quantum information processing in 1D wire networks. Nat. Phys. 7, 412–417 (2011).

    Article  Google Scholar 

  4. 4.

    Nayak, C., Simon, S. H., Stern, A., Freedman, M. & Das Sarma, S. Non-Abelian anyons and topological quantum computation. Rev. Mod. Phys. 80, 1083–1159 (2008).

    ADS  MathSciNet  Article  Google Scholar 

  5. 5.

    Kitaev, A. Y. Unpaired Majorana fermions in quantum wires. Phys. Uspekhi 44, 131 (2001).

    ADS  Article  Google Scholar 

  6. 6.

    Fu, L. & Kane, C. L. Superconducting proximity effect and Majorana fermions at the surface of a topological insulator. Phys. Rev. Lett. 100, 096407 (2008).

    ADS  Article  Google Scholar 

  7. 7.

    Beenakker, C. W. J. Search for Majorana fermions in superconductors. Annu. Rev. Condens. Mat. Phys. 4, 113–136 (2013).

    ADS  Article  Google Scholar 

  8. 8.

    Xu, J. P. et al. Experimental detection of a Majorana mode in the core of a magnetic vortex inside a topological insulator–superconductor Bi2Te3/NbSe2 heterostructure. Phys. Rev. Lett. 114, 017001 (2015).

    ADS  Article  Google Scholar 

  9. 9.

    Wang, D. F. et al. Evidence for Majorana bound states in an iron-based superconductor. Science 362, 333–335 (2018).

    ADS  Article  Google Scholar 

  10. 10.

    Machida, T. et al. Zero-energy vortex bound state in the superconducting topological surface state of Fe(Se,Te). Nat. Mater. 18, 811–815 (2019).

    ADS  Article  Google Scholar 

  11. 11.

    Zhang, P. et al. Observation of topological superconductivity on the surface of an iron-based superconductor. Science 360, 182–186 (2018).

    ADS  Article  Google Scholar 

  12. 12.

    Wang, Z. J. et al. Topological nature of the FeSe0.5Te0.5 superconductor. Phys. Rev. B 92, 115119 (2015).

    ADS  Article  Google Scholar 

  13. 13.

    Xu, G., Lian, B., Tang, P. Z., Qi, X. L. & Zhang, S. C. Topological superconductivity on the surface of Fe-based superconductors. Phys. Rev. Lett. 117, 047001 (2016).

    ADS  Article  Google Scholar 

  14. 14.

    Yin, J. X. et al. Observation of a robust zero-energy bound state in iron-based superconductor Fe(Te,Se). Nat. Phys. 11, 543–546 (2015).

    Article  Google Scholar 

  15. 15.

    Jiang, K., Dai, X. & Wang, Z. Q. Quantum anomalous vortex and Majorana zero mode in iron-based superconductor Fe(Te,Se). Phys. Rev. X 9, 011033 (2019).

    Google Scholar 

  16. 16.

    Mourik, V. et al. Signatures of Majorana fermions in hybrid superconductor–semiconductor nanowire devices. Science 336, 1003–1007 (2012).

    ADS  Article  Google Scholar 

  17. 17.

    Das, A. et al. Zero-bias peaks and splitting in an Al–InAs nanowire topological superconductor as a signature of Majorana fermions. Nat. Phys. 8, 887–895 (2012).

    Article  Google Scholar 

  18. 18.

    Deng, M. T. et al. Anomalous zero-bias conductance peak in a Nb–InSb nanowire–Nb hybrid device. Nano Lett. 12, 6414–6419 (2012).

    ADS  Article  Google Scholar 

  19. 19.

    Zhang, H. et al. Quantized Majorana conductance. Nature 556, 74–79 (2018).

    ADS  Article  Google Scholar 

  20. 20.

    Law, K. T., Lee, P. A. & Ng, T. K. Majorana fermion induced resonant Andreev reflection. Phys. Rev. Lett. 103, 237001 (2009).

    ADS  Article  Google Scholar 

  21. 21.

    Wimmer, M., Akhmerov, A. R., Medvedyeva, M. V., Tworzydlo, J. & Beenakker, C. W. J. Majorana bound states without vortices in topological superconductors with electrostatic defects. Phys. Rev. Lett. 105, 046803 (2010).

    ADS  Article  Google Scholar 

  22. 22.

    Li, F. S. et al. Interface-enhanced high-temperature superconductivity in single-unit-cell FeTe1-xSex films on SrTiO3. Phys. Rev. B 91, 220503 (2015).

    ADS  Article  Google Scholar 

  23. 23.

    Nichele, F. et al. Scaling of Majorana zero-bias conductance peaks. Phys. Rev. Lett. 119, 136803 (2017).

    ADS  Article  Google Scholar 

  24. 24.

    Liu, C. et al. Detection of a zero energy bound state induced on high temperature superconducting one-unit-cell FeSe on SrTiO3. Preprint at https://arxiv.org/abs/1807.07259 (2018).

  25. 25.

    Setiawan, F., Liu, C. X., Sau, J. D. & Das Sarma, S. Electron temperature and tunnel coupling dependence of zero-bias and almost-zero-bias conductance peaks in Majorana nanowires. Phys. Rev. B 96, 184520 (2017).

    ADS  Article  Google Scholar 

  26. 26.

    Qi, X. L., Hughes, T. L., Raghu, S. & Zhang, S. C. Time-reversal-invariant topological superconductors and superfluids in two and three dimensions. Phys. Rev. Lett. 102, 187001 (2009).

    ADS  Article  Google Scholar 

  27. 27.

    Zhang, F., Kane, C. L. & Mele, E. J. Time-reversal-invariant topological superconductivity and Majorana Kramers pairs. Phys. Rev. Lett. 111, 056402 (2013).

    ADS  Article  Google Scholar 

  28. 28.

    Nadj-Perge, S. et al. Observation of Majorana fermions in ferromagnetic atomic chains on a superconductor. Science 346, 602–607 (2014).

    ADS  Article  Google Scholar 

  29. 29.

    Kim, H. et al. Toward tailoring Majorana bound states in artificially constructed magnetic atom chains on elemental superconductors. Sci. Adv. 4, eaar5251 (2018).

    ADS  Article  Google Scholar 

  30. 30.

    Alff, L. et al. Spatially continuous zero-bias conductance peak on (110) YBa2Cu3O7-δ surfaces. Phys. Rev. B 55, R14757–R14760 (1997).

    ADS  Article  Google Scholar 

  31. 31.

    Sato, M., Tanaka, Y., Yada, K. & Yokoyama, T. Topology of Andreev bound states with flat dispersion. Phys. Rev. B 83, 224511 (2011).

    ADS  Article  Google Scholar 

  32. 32.

    Shi, X. et al. FeTe1−xSex monolayer films: towards the realization of high-temperature connate topological superconductivity. Sci. Bull. 62, 503–507 (2017).

    Article  Google Scholar 

  33. 33.

    Wei, P., Manna, S., Eich, M., Lee, P. & Moodera, J. Superconductivity in the surface state of noble metal gold and its Fermi level tuning by EuS dielectric. Phys. Rev. Lett. 122, 247002 (2019).

    ADS  Article  Google Scholar 

  34. 34.

    Wang, Q. Y. et al. Interface-induced high-temperature superconductivity in single-unit-cell FeSe films on SrTiO3. Chin. Phys. Lett. 29, 037402 (2012).

    ADS  Article  Google Scholar 

  35. 35.

    Qi, X. L., Hughes, T. L. & Zhang, S. C. Topological invariants for the Fermi surface of a time-reversal-invariant superconductor. Phys. Rev. B 81, 134508 (2010).

    ADS  Article  Google Scholar 

Download references

Acknowledgements

This work was supported by the National Natural Science Foundation of China (no. 11888101), the National Key Research and Development Program of China (2018YFA0305604 and 2017YFA0303302), the National Natural Science Foundation of China (no. 11774008), the Strategic Priority Research Program of the Chinese Academy of Sciences (grant no. XDB28000000), the Beijing Natural Science Foundation (Z180010) and the US Department of Energy, Basic Energy Sciences (grant no. DE-FG02–99ER45747: K.J. and Z.W.).

Author information

Affiliations

Authors

Contributions

J.W. conceived and supervised the research. C.C. grew the samples and analysed the experimental data. C.C., C.L. and Y.L. carried out the STM/STS experiments. K.J., Y.Z. and Z.W. proposed the theoretical model and performed the theoretical analysis and calculations. C.C., Z.W. and J.W. wrote the manuscript with comments from all authors.

Corresponding author

Correspondence to Jian Wang.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Figs. 1–9.

Source data

Source Data Fig. 1

Source data for Fig. 1.

Source Data Fig. 2

Source data for Fig. 2.

Source Data Fig. 3

Source data for Fig. 3.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Chen, C., Jiang, K., Zhang, Y. et al. Atomic line defects and zero-energy end states in monolayer Fe(Te,Se) high-temperature superconductors. Nat. Phys. 16, 536–540 (2020). https://doi.org/10.1038/s41567-020-0813-0

Download citation

Further reading