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

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, super-conductivity 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.We acknowledge the financial support from the European Union (ERC AdG Mol-2D 788222 and ERC-2015-AdG694097), the Spanish MICINN (MAT2017-89993-R cofinanced by FEDER and Excellence Unit "Mari ' a de Maeztu", CEX2019-000919-M), the Generalitat Valenciana (Prometeo program and PO FEDER Program, ref IDIFEDER/2018/061 and IDIFEDER/2020/063), the Basque government (Grupos Consolidados, IT1249-19) and the Deutsche Forschungsgemeinschaft (DFG) under Germany's Excellence Strategy Cluster of Excellence Advanced Imaging of Matter (AIM) EXC 2056-390715994 and funding by the Deutsche Forschungsgemeinschaft (DFG) under RTG 1995 and GRK 2247. Support by the Max Planck Institute -New York City Center for Non-Equilibrium Quantum Phenomena is acknowledged. R.C. acknowledges the support of a fellowship from "la Caixa" Foundation (ID 100010434). The fellowship code is LCF/BQ/PR19/11700008. J.J.B. thanks support from the Plan Gent of Excellence of the Generalitat Valenciana (CDEIGENT/2019/022). C.B.-C. thanks the Generalitat Valencia for a PhD fellowship