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Giant valley-Zeeman coupling in the surface layer of an intercalated transition metal dichalcogenide

Abstract

Spin–valley locking is ubiquitous among transition metal dichalcogenides with local or global inversion asymmetry, in turn stabilizing properties such as Ising superconductivity, and opening routes towards ‘valleytronics’. The underlying valley–spin splitting is set by spin–orbit coupling but can be tuned via the application of external magnetic fields or through proximity coupling. However, only modest changes have been realized to date. Here, we investigate the electronic structure of the V-intercalated transition metal dichalcogenide V1/3NbS2 using microscopic-area spatially resolved and angle-resolved photoemission spectroscopy. Our measurements and corresponding density functional theory calculations reveal that the bulk magnetic order induces a giant valley-selective Ising coupling exceeding 50 meV in the surface NbS2 layer, equivalent to application of a ~250 T magnetic field. This energy scale is of comparable magnitude to the intrinsic spin–orbit splittings, and indicates how coupling of local magnetic moments to itinerant states of a transition metal dichalcogenide monolayer provides a powerful route to controlling their valley–spin splittings.

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Fig. 1: Surface-termination-dependent electronic structure of V1/3NbS2.
Fig. 2: Low-energy electronic structure of the NbS2-terminated surface.
Fig. 3: Valley-dependent band splitting from magnetic exchange.
Fig. 4: Orbital-selective magnetic exchange coupling.

Data availability

The research data supporting this publication can be accessed at the University of St Andrews Research Portal: https://doi.org/10.17630/fb5496ed-6eae-49fa-9214-cd3507265f2b (ref. 40).

Code availability

The codes used in this study are available either publicly (Wannier90; http://www.wannier.org) or through subscription (Vienna Ab-initio Simulation Package; https://www.vasp.at). For a detailed description of input parameters used for each code, refer to the ‘Calculations’ section in the Methods. Further inquiries should be addressed to the corresponding authors.

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Acknowledgements

We thank M. Leandersson and T. Balasubramanian for useful discussions. We gratefully acknowledge support from the Leverhulme Trust (grant no. RL-2016-006; P.D.C.K., B.E., T.A., A.R. and C.B.), the European Research Council (through the QUESTDO project, 714193; P.D.C.K. and G.-R.S.), the Engineering and Physical Sciences Research Council (grant nos EP/T02108X/1 (P.D.C.K. and P.A.E.M.) and EP/N032128/1 (D.A.M. and G.B.)) and the Center for Computational Materials Science at the Institute for Materials Research for allocations on the MASAMUNE-IMR supercomputer system (project no. 202112-SCKXX-0510; R.V.B. and M.S.B.). S.B., E.A.M. and A.Z. gratefully acknowledge studentship support from the International Max-Planck Research School for Chemistry and Physics of Quantum Materials. We gratefully acknowledge the MAX IV Laboratory for time on the Bloch beamline under proposal nos 20200227, 20210091 and 20210763. Research conducted at MAX IV, a Swedish national user facility, is supported by the Swedish Research council under contract 2018-07152, the Swedish Governmental Agency for Innovation Systems under contract 2018-04969 and Formas under contract 2019-02496. The research leading to this result has been supported by the project CALIPSOplus under grant agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. For the purpose of open access, we have applied a Creative Commons Attribution (CC BY) licence to any Author Accepted Manuscript version arising.

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The ARPES data were measured by B.E., P.A.E.M., S.B., T.A., G.-R.S., A.R., E.A.M., A.Z., C.B. and P.D.C.K. and analysed by B.E.; O.D., R.V.B. and M.S.B. performed the DFT and tight-binding calculations. A.E.H., D.A.M. and G.B. grew and characterized the samples. C.M.P. and D.C. maintained the Bloch beamline and provided experimental support. B.E., O.D., M.S.B. and P.D.C.K. wrote the manuscript with input and contributions from all authors.

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Correspondence to M. S. Bahramy or P. D. C. King.

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Edwards, B., Dowinton, O., Hall, A.E. et al. Giant valley-Zeeman coupling in the surface layer of an intercalated transition metal dichalcogenide. Nat. Mater. (2023). https://doi.org/10.1038/s41563-022-01459-z

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