Optical investigation of many-body interactions in transition metal dichalcogenide heterostructures

Abstract

Two-dimensional transition metal dichalcogenide (TMD) heterostructures have emerged as a novel platform for the investigation of many-body physical phenomena. In these systems, tightly bound excitons dressed by a gate-tunable Fermi sea form exciton-polarons, which are sensitive to Coulomb and spin interactions. In addition, TMD moir´e devices provide a highly tunable platform to study strongly correlated electronic states. This thesis describes the use of magneto-optical polarisation-resolved white-light confocal reflection spectroscopy at cryogenic temperatures (4 K) to probe different many-body interactions in TMD heterostructure devices. First, monolayer and bilayer tungsten diselenide (WSe2) and molybdenum diselenide (MoSe2) are investigated under varying carrier concentration. The doping dependent dispersions of the exciton-polarons are shown to be excellent probes of the distinctive band structures of these materials. Then, in a moir´e heterobilayer MoSe2/WSe2 structure, optically injected excitons are shown to interact with itinerant carriers occupying narrow moir´e bands to form exciton-polarons sensitive to strong correlations. At a multitude of fractional fillings of the moir´e lattice, the ordering of both electrons and holes into stable correlated electronic states is observed, leading to extraordinary Zeeman splittings of the exciton-polarons. Next, in heterotrilayer bilayer WSe2/monolayer MoSe2, the energetic ordering of the moir´e bands is shown to be highly tunable with applied vertical electric field, leading to the demonstration of hole transfer between correlated states in K and Γ valley derived moir´e bands. Finally, the moire lattice uniformity of MoSe2/WSe2 moir´e heterostructures is probed by spatial mapping of the electronic correlations, leading to a measured variation in twist angle of 0.6 degrees across the device. These results establish WSe2 and MoSe2 heterostructures as an exciting platform for investigations of exciton-polarons, Fermi-Hubbard or Bose-Hubbard physics.