Tuning metal/superconductor to insulator/superconductor coupling via control of proximity enhancement between NbSe$_2$ monolayers

TL;DR

This study demonstrates how stacking metal and superconductor monolayers, specifically NbSe$_2$, with atomic precision can tune the superconductive coupling from proximity-enhanced to tunneling-dominated, revealing a crossover between different electronic regimes.

Contribution

It introduces a method to control superconductive coupling in layered materials by adjusting spacer layer thickness, enabling transition from metallic to insulating regimes in superconductor heterostructures.

Findings

Superconductive coupling can be tuned from proximity-enhanced to tunneling-dominated.

Critical fields indicate increased coherence lengths and two-dimensional superconductivity.

Identified three regimes: metallic, disordered-metallic, and insulating with Josephson tunneling.

Abstract

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)$_{1+{\delta}}$]$_m$[NbSe$_2$]$_1$ tailored multilayers with varying SnSe layer thickness. From high-field magnetotransport the critical fields yield Ginzburg-Landau coherence lengths with an increase of 140 % cross-plane , trending towards two-dimensional superconductivity for m > 9. We show cross-over between three regimes: metallic with proximity-enhanced coupling, disordered-metallic with intermediate coupling and insulating with Josephson tunneling. 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.