Correlations and topology in a transition metal dichalcogenide compound

A small change in the crystal structure of a material can completely modify its electronic properties. This is the case in the transition metal dichalcogenide TaS2 where a slight rotation of the sulphur atoms from the octahedral 1T structure to the trigonal prismatic 1H varies it from a superconductor to a Mott insulator possibly hosting a spin liquid state. We have studied 4Hb-TaS2 that interleaves the 1T and 1H polytypes. This has allowed us to investigate using scanning tunnelling spectroscopy the fate of a Mott insulator when coupled to a metal and the superconducting phase that results from sandwiching it with Mott insulating layers. In the former we find a quantum phase transition that can be induced by the STM tip, electric field and temperature which possibly signifies the onset of correlations among Anderson impurities (or of a Kondo lattice). In the latter we identify a topological nodal superconducting state which we attribute to interaction-promoted inter-orbital pairing.