Alternating superconducting and charge density wave monolayers within bulk 6R-TaS2

TL;DR

This study reports a bulk van der Waals heterostructure of alternating superconducting and charge density wave monolayers in 6R-TaS2, showing enhanced superconducting transition temperature and insights into layer-specific properties.

Contribution

It demonstrates a novel bulk vdW heterostructure with alternating monolayers of different phases, created via phase transition, and provides first-principles insights into their combined properties.

Findings

Superconducting transition temperature (Tc) is 2.6 K, higher than bulk 2H-TaS2.

Exfoliation and restacking increase Tc to 3.6 K.

Electron microscopy confirms alternating monolayers within 6R-TaS2.

Abstract

Van der Waals (vdW) heterostructures continue to attract intense interest as a route of designing materials with novel properties that cannot be found in naturally occurring materials. Unfortunately, this approach is currently limited to only a few layers that can be stacked on top of each other. Here we report a bulk material consisting of superconducting monolayers interlayered with monolayers displaying charge density waves (CDW). This bulk vdW heterostructure is created by phase transition of 1T-TaS2 to 6R at 800 {\deg}C in an inert atmosphere. Electron microscopy analysis directly shows the presence of alternating 1T and 1H monolayers within the resulting bulk 6R phase. Its superconducting transition (Tc) is found at 2.6 K, exceeding the Tc of the bulk 2H phase of TaS2. The superconducting temperature can be further increased to 3.6 K by exfoliating 6R-TaS2 and then restacking its layers. Using first-principles calculations, we argue that the coexistence of superconductivity and CDW within 6R-TaS2 stems from amalgamation of the properties of adjacent 1H and 1T monolayers, where the former dominates the superconducting state and the latter the CDW behavior.