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Observation of spin-momentum locked surface states in amorphous Bi2Se3

Abstract

Crystalline symmetries have played a central role in the identification and understanding of quantum materials. Here we investigate whether an amorphous analogue of a well known three-dimensional strong topological insulator has topological properties in the solid state. We show that amorphous Bi2Se3 thin films host a number of two-dimensional surface conduction channels. Our angle-resolved photoemission spectroscopy data are consistent with a dispersive two-dimensional surface state that crosses the bulk gap. Spin-resolved photoemission spectroscopy shows this state has an anti-symmetric spin texture, confirming the existence of spin-momentum locked surface states. We discuss these experimental results in light of theoretical photoemission spectra obtained with an amorphous topological insulator tight-binding model, contrasting it with alternative explanations. The discovery of spin-momentum locked surface states in amorphous materials opens a new avenue to characterize amorphous matter, and triggers the search for an overlooked subset of quantum materials outside of current classification schemes.

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Fig. 1: Structural and spectral evidence for the amorphous atomic structure of Bi2Se3.
Fig. 2: Electron transport in amorphous Bi2Se3.
Fig. 3: ARPES spectra of electronic states in amorphous Bi2Se3.
Fig. 4: Spin-resolved ARPES spectra of electronic states in amorphous Bi2Se3.

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All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Information. Additional data related to this paper may be requested from the authors.

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Acknowledgements

P.C. and S.C. thank E. Parsonnet and D. Rees for their discussions. A.G.G. is grateful to J. H. Bardarson, S. Ciuchi, S. Fratini and Q. Marsal for discussions. D.V. thanks A. Akhmerov, A. Lau and P. Perez Piskunow for discussions. The project was primarily funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under contract no. DE-AC02-05-CH11231 within the Nonequilibrium Magnetic Materials Program (MSMAG). The ARPES and spin-resolved ARPES work was supported by the Lawrence Berkeley National Laboratory’s Ultrafast Materials Science programme, funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under contract no. DE-AC02-05-CH11231. TEM at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences of the US Department of Energy under contract no. DE-AC02-05CH11231. Computational resources were provided by the National Energy Research Scientific Computing Center and the Molecular Foundry, US Department of Energy Office of Science User Facilities supported by the Office of Science of the US Department of Energy under contract no. DE-AC02-05CH11231. The work performed at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences of the US Department of Energy under the same contract. P.C. is supported by the National Science Foundation Graduate Research Fellowship under grant no. 1752814. S.C. was supported by the National Science Foundation Graduate Research Fellowship under grant nos DGE1852814 and DGE1106400. A.G.G. is supported by the French National Research Agency (ANR) under grant ANR-18-CE30-0001-01 and the European Union Horizon 2020 research and innovation programme under grant agreement no. 829044. D.V. is supported by Dutch Research Council (NWO) Vidi programme grant 680-47-53. S.Z. was supported by the National Science Foundation under STROBE grant no. DMR 1548924.

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Contributions

P.C. and S.C. contributed equally to this work. The project was initiated and overseen by P.C., S.C., A.G.G., A.L. and F.H.; P.C. grew the films. S.C. performed the synchrotron ARPES, S.C. and P.C. performed the spin-resolved ARPES measurements and S.C. performed the data analysis. P.C. performed the transport measurements. S.Z., E.K., S.C. and P.C. performed the TEM. M.M.-R. and P.C. performed the Raman measurements. Z.C. performed the molecular dynamics, and S.M.G. performed the density-of-states calculations. A.G.G. and D.V. constructed the tight-binding model, and D.V. performed the numerical calculations. P.C., S.C., A.G.G. and D.V. took part in interpreting the results. All authors contributed to writing the manuscript.

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Correspondence to Paul Corbae.

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Corbae, P., Ciocys, S., Varjas, D. et al. Observation of spin-momentum locked surface states in amorphous Bi2Se3. Nat. Mater. (2023). https://doi.org/10.1038/s41563-022-01458-0

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