Quantum Matter Seminar

In person attendance

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 trigonal prismatic 1H structure to the octahedral 1T 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 tunneling spectroscopy both the nature of the resulting superconductor as well as the fate of a Mott insulator when coupled to a metal. We find a topological nodal superconductor manifested by a variety of boundary modes. Instead of a Mott insulator we find a sharp first order quantum phase transition between a flat band and a Kondo cluster states. It is induced by the combination of electric field and temperature as well as by tuning the inter-layer coupling with the STM tip. The 4Hb-Tas2 system can be thus used as a platform to study the evolution of Kondo lattice from isolated Kondo impurities via an intermediate correlated Kondo cluster state and its coupling to superconductivity.