Preferential out-of-plane conduction and quasi-one-dimensional electronic states in layered 1T-TaS2

TL;DR

This paper reveals that 1T-TaS2 exhibits out-of-plane metallic conduction and quasi-one-dimensional electronic states, challenging the typical quasi-two-dimensional classification of layered TMDs and suggesting a new perspective on its metal-insulator transition.

Contribution

It demonstrates that 1T-TaS2 defies the common anisotropic behavior of TMDs, showing out-of-plane metallicity and quasi-one-dimensional electronic structure supported by ab-initio calculations.

Findings

Out-of-plane conduction in 1T-TaS2 is metallic.

Resistivity anisotropy in 1T-TaS2 is close to one.

The metal-insulator transition is a quasi-one-dimensional instability.

Abstract

Layered transition metal dichalcogenides (TMDs) are commonly classified as quasi-two-dimensional materials, meaning that their electronic structure closely resembles that of an individual layer, which results in resistivity anisotropies reaching thousands. Here, we show that this rule does not hold for 1T-TaS2 - a compound with the richest phase diagram among TMDs. While the onset of charge density wave order makes the in-plane conduction non-metallic, we reveal that the out-of-plane charge transport is metallic and the resistivity anisotropy is close to one. We support our findings with ab-initio calculations predicting a pronounced quasi-one-dimensional character of the electronic structure. Consequently, we interpret the highly debated metal-insulator transition in 1T-TaS2 as a quasi-one-dimensional instability, contrary to the long-standing Mott localisation picture. In a broader context, these findings are relevant for the newly born field of van der Waals heterostructures, where tuning interlayer interactions (e.g. by twist, strain, intercalation, etc.) leads to new emergent phenomena.