Out-of-Plane Transport of 1T-TaS2/Graphene-Based van der Waals Heterostructures.

Carla Boix-Constant,José J Baldoví,Samuel Mañas-Valero,Ángel Rubio,Eugenio Coronado,Rosa Córdoba

doi:10.1021/acsnano.1c03012

Abstract

Due to their anisotropy, layered materials are excellent candidates for studying the interplay between the in-plane and out-of-plane entanglement in strongly correlated systems. A relevant example is provided by 1T-TaS2, which exhibits a multifaceted electronic and magnetic scenario due to the existence of several charge density wave (CDW) configurations. It includes quantum hidden phases, superconductivity and exotic quantum spin liquid (QSL) states, which are highly dependent on the out-of-plane stacking of the CDW. In this system, the interlayer stacking of the CDW is crucial for interpreting the underlying electronic and magnetic phase diagram. Here, atomically thin-layers of 1T-TaS2 are integrated in vertical van der Waals heterostructures based on few-layers graphene contacts and their electrical transport properties are measured. Different activation energies in the conductance and a gap at the Fermi level are clearly observed. Our experimental findings are supported by fully self-consistent DFT+U calculations, which evidence the presence of an energy gap in the few-layer limit, not necessarily coming from the formation of out-of-plane spin-paired bilayers at low temperatures, as previously proposed for the bulk. These results highlight dimensionality as a key effect for understanding quantum materials as 1T-TaS2, enabling the possible experimental realization of low-dimensional QSLs.

Highlights

Due to their anisotropy, layered materials are excellent candidates for studying the interplay between the inplane and out-of-plane entanglement in strongly correlated systems
From I-charge density wave (CDW) to N-CDW at 350 K, from N-CDW to C-CDW at 200 K, from C-CDW to H-CDW at ca. 50 K and the quantum spin liquid (QSL) crossovers described at 100 K and 25 K. (d) scanning transmission electron microscopy (STEM) image of a van der Waals heterostructures (vdWHs) showing 5 layers of 1T-TaS2
Scale bar: 5 nm. (e) Comparative of in-plane and out-ofplane transport measurements on 1T-TaS2 atomically thin layers

Summary

Introduction

Due to their anisotropy, layered materials are excellent candidates for studying the interplay between the inplane and out-of-plane entanglement in strongly correlated systems. A relevant example is provided by 1T-TaS2, which exhibits a multifaceted electronic and magnetic scenario due to the existence of several charge density wave (CDW) configurations It includes quantum hidden phases, superconductivity and exotic quantum spin liquid (QSL) states, which are highly dependent on the out-of-plane stacking of the CDW. Our experimental findings are supported by fully self-consistent DFT+U calculations, which evidence the presence of an energy gap in the few-layer limit, not necessarily coming from the formation of out-of-plane spin-paired bilayers at low temperatures, as previously proposed for the bulk These results highlight dimensionality as a key effect for understanding quantum materials as 1T-TaS2, enabling the possible experimental realization of low-dimensional QSLs. Low-dimensional materials offer appealing examples for studying strongly correlated materials with tantalizing physical phenomena such as superconductivity or magnetism.[1−3] A relevant example in this context is provided by transition metal dichalcogenides (TMDCs). Different interlayer mechanisms have been proposed and the conventional Mott picture, dimerization and the formation of domain wall networks, among others, are being revisited.[27−31] Theoretically, some authors have proposed metallic band dispersion along the out-of-plane direction if the Stars-of-David are coupled vertically (A stacking, Figure 1c), or through a diagonal

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Conclusion