Abstract
Polytypism in transition metal dichalcogenides (TMDs) introduces an additional degree of freedom for tailoring the electronic properties of layered van der Waals materials. Polytypes with larger unit cells, spanning four or six layers, can be viewed as natural homostructures, since their atomic composition remains identical across the layers. The resultant crystalline environments can potentially give rise to exotic electronic states, earning these materials recent attention. In this study, we examine structural and charge transport properties of metallic and superconducting 4Ha-NbSe2. We find that the compound has a highly disordered stacking of layers, which impedes interlayer coherence, as demonstrated by detailed out-of-plane resistivity measurements, and effectively tunes the bulk system towards an atomically thin limit. The disordered structure largely accounts for the enhanced resistivity anisotropy and superconducting upper critical field, when compared to 2Ha-NbSe2. This phenomenon can be exploited to promote quasi-two-dimensional physics in bulk crystals, and our study also underscores the importance of thorough structural characterization when investigating large-unit-cell polytypes of TMDs.
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Data supporting the results of this paper can be provided by K.S. upon a reasonable request.
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Acknowledgements
E.M., K.S., and L.F. disclose the support of this work by the Swiss National Science Foundation through its SINERGIA network MPBH and grants No. 200021_175836 and PP00P2_170544.
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E.M. and A.A. conducted the X-ray measurements. A.A. and Y.P. analyzed and interpreted the crystallographic data. H.B. produced the crystals of 2Ha-NbSe2 and 4Ha-NbSe2. E.M. and M.K. prepared the samples for resistivity measurements, which were conducted by E.M. and K.S., who also analyzed the data. E.M., L.F., and K.S. wrote the manuscript. The project was directed by L.F. and K.S.
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Martino, E., Arakcheeva, A., Berger, H. et al. Towards atomically-thin regime in bulk 4H-NbSe2 with interlayer disorder. npj 2D Mater Appl (2026). https://doi.org/10.1038/s41699-025-00659-w
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DOI: https://doi.org/10.1038/s41699-025-00659-w
