UC San Diego

Spatially indirect excitons (IXs), also known as interlayer excitons, are bound pairs of an electron and a hole in spatially separated layers. IXs can propagate over long distances before they recombine into light, and they can cool down below the temperature of quantum degeneracy within their lifetimes, which can be controlled by gate voltage up to microseconds and beyond. These properties make IXs a promising platform for studying fundamental physics phenomena and as the medium for highly efficient signal processing devices. IXs were originally studied in gallium arsenide (GaAs) heterostructures, where IXs have shown evidence for Bose-Einstein condensation, and proof of principle has been demonstrated for excitonic transistors and excitonic integrated circuits. IXs only exist at low temperatures in GaAs systems due to the low IX binding energy on the order of 10 meV. In the transition-metal dichalcogenide (TMD) heterostructure system, the IX binding energy is predicted to be more than two orders of magnitude higher, making IXs stable at room temperature and allowing for the possibility of high temperature IX superfluidity. To date, observation of some of the key IX behaviors, namely the long-range IX transport and evidence of IX condensation, has remained elusive in the TMD system. This dissertation characterizes the IX spectrum in a MoSe2/WSe2 heterostructure, demonstrates the realization and control of long-range IX propagation using a new mechanism beyond the know mechanism for IX control in GaAs heterostructures, and separately identifies a quantum origin for the propagation of IXs generated by resonant excitation in the TMD heterostructure.