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Half-integer level shift of vortex bound states in an iron-based superconductor

An Author Correction to this article was published on 13 March 2020

An Author Correction to this article was published on 13 March 2020

This article has been updated

Abstract

Vortices in topological superconductors may host Majorana zero modes (MZMs), which have been proposed as the building blocks of fault-tolerant topological quantum computers. Recently, a new single-material platform with the potential for realizing MZMs has been discovered in iron-based superconductors, without involving hybrid semiconductor–superconductor structures. Here, we report a detailed scanning tunnelling spectroscopy study of a FeTe0.55Se0.45 single crystal and show that this material hosts two distinct classes of vortex. These differ by a half-integer level shift in the energy spectra of the vortex bound states. This level shift is directly tied to the presence or absence of a zero-bias conductance peak and also alters the ratios of higher energy levels from integer to half-odd-integer. Our model calculations fully reproduce the spectra of these two types of vortex bound state, suggesting the presence of regions with and without topological surface states, which coexist within the same crystal. Our findings provide strong evidence for the presence of MZMs in FeTe0.55Se0.45 and establish it as an excellent platform for further studies.

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Fig. 1: CBSs in a vortex with MZM.
Fig. 2: Integer quantized CBSs in a topological vortex.
Fig. 3: Half-odd-integer quantized CBSs in an ordinary vortex.
Fig. 4: Spatial pattern of integer quantized CBSs.
Fig. 5: Half-integer level shift around a MZM.

Data availability

The data that support the findings of this study are available from the corresponding authors on reasonable request.

Change history

  • 13 March 2020

    An amendment to this paper has been published and can be accessed via a link at the top of the paper.

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Acknowledgements

We thank N.F. Yuan, C.-K. Chiu, C. Schrade, S.-S. Qin and R.-X. Zhang for helpful discussions and F.-Z. Yang, G.-J. Qian for technical assistance. The work at IOP is supported by grants from the Ministry of Science and Technology of China (2015CB921000, 2015CB921300 and 2016YFA0202300), the National Natural Science Foundation of China (11234014, 11574371 and 61390501), and the Chinese Academy of Sciences (XDB28000000 and XDB07000000). The work at MIT is supported by DOE Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under award no. DE-SC0019275. G.D.G. is supported by US DOE DE-SC0012704. J.S. and R.D.Z. are supported by the Center for Emergent Superconductivity, an EFRC funded by the US DOE.

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H.D. and H.-J.G. designed the experiments. S.Z., L.C., H.C. and Y.X. performed the STM experiments with assistance from L.K., W.L., D.W., P.F. and S.D. M.P., H.I. and L.F. provided theoretical models and simulations. J.S., R.Z. and G.D.G. provided samples. L.K., S.Z. and H.D. analysed experiment data with input from all other authors. L.K., M.P. and S.Z. plotted figures with input from all other authors. All authors participated in writing the manuscript. H.D., H.-J.G. and L.F. supervised the project.

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Correspondence to Liang Fu, Hong-Jun Gao or Hong Ding.

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Supplementary Information

Additional theoretical and experimental details, Supplementary Figs. 1–11 and refs. 1–41.

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Kong, L., Zhu, S., Papaj, M. et al. Half-integer level shift of vortex bound states in an iron-based superconductor. Nat. Phys. 15, 1181–1187 (2019). https://doi.org/10.1038/s41567-019-0630-5

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