Tuning metal/superconductor to insulator/superconductor coupling via control of proximity enhancement between NbSe 2 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+δ ] m [NbSe 2 ] 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-over 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.