Stacking-tuned superconductivity and competing charge-density-wave states in NbSe₂

2026/07/22 by Sandra Sajan, Xinze Yang, Haojie Guo +9
#cond-mat.supr-con

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Abstract

Layer stacking provides a powerful yet underexplored route for reshaping collective quantum order in van der Waals materials. Here we use high-resolution scanning tunneling microscopy and spectroscopy to show that the stacking sequence alone can qualitatively transform the charge density and superconducting orders in NbSe₂, while preserving the same in-plane atomic structure. Comparing the 4Ha and 2H polytypes, we find that, unlike the ubiquitous triangular incommensurate 3Q^I order of 2H-NbSe₂, 4Ha-NbSe₂ hosts two competing CDW states with no measurable correlation with local strain: a unidirectional commensurate 1Q^C phase and a triangular incommensurate 3Q^I phase, with Q^I=Q^C+δ. We introduce a phase-resolved analysis that directly maps the gradient of the CDW phases and reveals vortices bound to the 1Q^C - 3Q^I phase boundaries. These vortices accommodate the momentum mismatch δ through abrupt 2π phase slips, providing a mechanism by which distinct charge orders coexist. Superconductivity is also reshaped by stacking, while both polytypes exhibit multiband pairing.

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