Two-dimensional (2D) crystals, such as graphene or transition metal dichalcogenides (TMDCs) are a fascinating class of quantummaterials. These compounds are obtained isolating the single atomic sheets that normally form bulk layered crystals, and the reduced dimensionality endows them with unique physical properties. These peculiar characteristics have made them a very interesting research topic, with potential for fundamental discoveries but also technological applications.
This thesis focuses on the behavior of excitons in artificial crystals composed of semiconducting two-dimensional materials of the TMDC family, which possess unusual spin- and valley-dependent optical and transport characteristics. The aim is to engineer their properties and build 2D heterostructures to investigate exciton dynamics and transport for applications in energy-efficient information technologies. To this end, the first part of the dissertation explores the transport mechanisms of indirect excitons inWSe2/MoSe2 heterobilayers. By resolving their motion in the time and space domain, one finds that IX travel with a superdiffusive trend, with increasing diffusivity coefficient as time elapses. This results in an efficient transport mechanismthat effectively depletes the exciton population from the excitation region. We study this mechanism as a function of the generated exciton density and temperature, revealing how the exciton-exciton interaction further enhances the observed superdiffusive transport mechanism. The second part of the thesis instead deals with interaction between cavity-photons and indirect excitons inWSe2/MoSe2 heterobilayers.
We exploit the field-effect energy tunability, to dynamically decrease the cavity-exciton detuning. When the exciton and cavity energy coincide, the interlayer exciton lifetime and emitted PL intensity are both enhanced. Analysing their angular radiation pattern, corroborated by transfer-matrix simulations, we decompose the contribution of in-plane and out-of-plane transition dipoles on the overall recorded PL signature. This allows us to understand the modulation on the spontaneous emission rate that the cavity induces on IX, effectively demonstrating a new photonic tuning of these versatile quasiparticles. The last part of this work focuses on themodulation of the exciton-exciton interactions in layer-hybridized interlayer excitons in homobilayers of WSe2. Here we show in a field-effect structure, that we can effectively modulate the dipole length of these excitonic
ensembles, with significant alterations of their many-body interactions. By analysing their motion in the time and space domain, we observe larger repulsive interactions for ensembles characterized by larger dipole moment lengths, in good agreement with our theoretical framework. Finally we show that differently from indirect excitons in other material platforms, this species features a power-independent emission quantum yield, which is an attractive feature the realization of efficient excitonic devices. These results further the current understanding of interlayer exciton dynamics, proposing novel schemes for their manipulation.