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.