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

Layered metallic transition-metal dichalcogenides are conventionally seen as two-dimensional conductors, despite a scarcity of systematic studies of the interlayer charge transport. Motivated by the ascending strategy of functionalizing 2D materials by vertical heterostructures we initiated an in-depth study of out-of-plane charge dynamics and emergent properties arising from interlayer coupling.
Here, we reveal c-axis-oriented quasi-one-dimensional electronic states in 1T-TaS₂, a layered system hosting a plethora of diverse phases, by probing its out-of-plane electrical resistivity using focused-ion-beam-tailored crystals. The in-plane conduction appears non-metallic due to presence of a unique nanoarray of charge density wave (CDW) domains. All the while, the interlayer resistivity has a metallic temperature dependence with the anisotropy close to one, as a result of intertwining of the orbital and CDW orders. The compound is known for what was believed to be a Mott-type localisation below 150 K. Yet with our data, supplemented by ab-initio calculations, we interpret the transition as a Peierls-like instability of the quasi-one-dimensional electronic structure. Our findings present a very unintuitive behaviour in a van der Waals crystal.