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Evidence of anisotropic Majorana bound states in 2M-WS2

Abstract

Searching for Majorana bound states has become an important topic because of its potential applications in topological quantum computing. 2M-phase WS2, a newly synthesized superconductor, not only presents the highest superconducting transition temperature (Tc = 8.8 K) among the intrinsic transition metal dichalcogenides but also is predicted to be a promising candidate as a topological superconductor. Using scanning tunnelling microscopy, we observe a U-shaped superconducting gap in 2M-WS2. Probable Majorana bound states are observed in magnetic vortices, which manifest as a non-split zero-energy state coexisting with the ordinary Caroli–de Gennes–Matricon bound states. Such non-split bound states in 2M-WS2 show highly spatial anisotropy, originating from the anisotropy of the superconducting order parameter and Fermi velocity. Due to its simple layered structure and substitution-free lattice, 2M-WS2 can be a building block to construct novel heterostructures and provides an ideal platform for the study of Majorana bound states.

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Fig. 1: Structure and superconductivity of WS2.
Fig. 2: Majorana and Caroli–de Gennes–Matricon bound states in a vortex core.
Fig. 3: Energy-dependent spatial distribution of in-gap bound states.
Fig. 4: Two types of spatial evolution of bound states near vortex cores.
Fig. 5: Effects of magnetic field on superconductivity.
Fig. 6: Robustness of superconductivity to intrinsic impurities.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

We thank Y. Zhang and Z. Wang for helpful discussions. The experimental work was supported by the National Science Foundation (nos. 11674191 and 11674165), the Ministry of Science and Technology of China (no. 2016YFA0301002) and the Beijing Advanced Innovation Center for Future Chip (ICFC), the National Key R&D Program of China (grant no. 2016YFB0901600), the Science and Technology Commission of Shanghai (grant no. 16JC1401700) and the CAS Center for Excellence in Superconducting Electronics. W.L. was also supported by the Tsinghua University Initiative Scientific Research Program, Beijing Young Talents Plan and the National Thousand-Young-Talents Program.

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W.L., F.H. and Q.-K.X. designed and coordinated the experiments. Y.Y. and X.W. carried out the STM experiments, and J.P. and Y.F. grew the samples. H.Z., X.M., K.H., L.W. and C.S. contributed to discussions about the data. W.L. and Y.Y. wrote the manuscript with comments from all authors.

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Correspondence to Fuqiang Huang or Wei Li or Qi-Kun Xue.

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Additional theoretical and experimental details, Supplementary Figs. 1–10 and Supplementary references 1–3.

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Yuan, Y., Pan, J., Wang, X. et al. Evidence of anisotropic Majorana bound states in 2M-WS2. Nat. Phys. 15, 1046–1051 (2019). https://doi.org/10.1038/s41567-019-0576-7

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