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# Electronic properties of the bulk and surface states of Fe1+yTe1−xSex

## Abstract

The idea of employing non-Abelian statistics for error-free quantum computing ignited interest in reports of topological surface superconductivity and Majorana zero modes (MZMs) in FeTe0.55Se0.45. However, the topological features and superconducting properties are not observed uniformly across the sample surface. The understanding and practical control of these electronic inhomogeneities present a prominent challenge for potential applications. Here, we combine neutron scattering, scanning angle-resolved photoemission spectroscopy, and microprobe composition and resistivity measurements to characterize the electronic state of Fe1+yTe1−xSex. We establish a phase diagram in which the superconductivity is observed only at sufficiently low Fe concentration, in association with distinct antiferromagnetic correlations, whereas the coexisting topological surface state occurs only at sufficiently high Te concentration. We find that FeTe0.55Se0.45 is located very close to both phase boundaries, which explains the inhomogeneity of superconducting and topological states. Our results demonstrate the compositional control required for use of topological MZMs in practical applications.

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## Data availability

All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Information. Additional data are available from the corresponding author upon reasonable request.

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## Acknowledgements

We gratefully acknowledge discussions with M. Lumsden, A. Tsvelik, A. Balatsky, Q. Li and X. Wang, and technical assistance from F. Loeb and M. K. Graves-Brook. This work at the Brookhaven National Laboratory (BNL) was supported by the Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, United States Department of Energy (US DOE), under contract no. DE-SC0012704. Work at BNL’s Center for Functional Nanomaterials was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, US DOE, under the same contract. This research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory.

## Author information

Authors

### Contributions

I.A.Z. conceived and directed the study. I.A.Z. and Y.L. designed the study with input from J.M.T. and P.D.J.; G.G., Z.X. and C.P. provided the samples for the study. I.A.Z., Y.L., D.F., A.T.S. and V.O.G. carried out neutron experiments and obtained the neutron data. N.Z. carried out ARPES measurements and initial ARPES analysis; Y.L. performed fitting of ARPES spectra. Y.L. performed local EDS and microprobe measurements with help from F.C. Y.L. and I.A.Z. analysed the data, prepared the figures and wrote the paper, with input from all authors.

### Corresponding author

Correspondence to Igor A. Zaliznyak.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

Peer review Information Nature Materials thanks Donglai Feng and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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

## Supplementary information

### Supplementary Information

Supplementary Figs. 1–12 and discussion.

## Rights and permissions

Reprints and Permissions

Li, Y., Zaki, N., Garlea, V.O. et al. Electronic properties of the bulk and surface states of Fe1+yTe1−xSex. Nat. Mater. 20, 1221–1227 (2021). https://doi.org/10.1038/s41563-021-00984-7

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• DOI: https://doi.org/10.1038/s41563-021-00984-7

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