Tuning metal/superconductor to insulator/superconductor coupling via control of proximity enhancement between NbSe₂ monolayers

The interplay between charge transfer and electronic disorder in transition-metal dichalcogenide multilayers gives rise to superconductive coupling driven by proximity enhancement, tunneling and superconducting fluctuations, of a yet unwieldy variety. Artificial spacer layers introduced with atomic precision change the density of states by charge transfer. Here, we tune the superconductive coupling between NbSe(2 )monolayers from proximity-enhanced to tunneling-dominated. We correlate normal and superconducting properties in [(SnSe)(1+d)](m)[NbSe2](1) tailored multilayers with varying SnSe layer thickness (m = 1 - 15). From high-field magnetotransport the critical fields yield Ginzburg-Landau coherence lengths with an increase of 140% cross-plane (m = 1 - 9), trending towards two-dimensional superconductivity for m > 9. We show cross-overs between three regimes: metallic with proximity-enhanced coupling (m = 1 - 4), disordered-metallic with intermediate coupling (m = 5 - 9) and insulating with Josephson tunneling (m > 9). Our results demonstrate that stacking metal mono-and dichalcogenides allows to convert a metal/superconductor into an insulator/superconductor system, prospecting the control of two-dimensional superconductivity in embedded layers.