EXCITONIC AND ELECTRONIC STATES IN VAN DER WAALS HETEROSTRUCTURES

Abstract

Two-dimensional transition metal dichalcogenides (TMDs) and their van der Waals (vdW) heterostructures provide a highly tunable platform for engineering excitonic, photonic, and correlated electronic states at the atomic limit. This dissertation investigates interaction-driven phenomena in TMD heterostructures through optical spectroscopy, electrostatic gating, nanocavity engineering, and low-temperature transport measurements.First, exciton–photon coupling is explored in atomically thin mirror nanocavities formed from two resonance-matched monolayer MoSe2 mirrors. In this device architecture, the monolayer TMDs serve not only as active excitonic media but also as the fundamental optical mirrors of the cavity. The excitonic origin of the mirror response gives rise to a nearly dispersionless cavity mode, distinguishing the system from conventional Fabry–Pérot cavities. Magnetic-field-dependent reflectance measurements further reveal chiral cavity modes arising from valley-selective optical transitions and the valley Zeeman effect. Electrical gating provides additional control over the excitonic resonance, enabling tunability of the confined optical mode. Second, gate-tunable exciton–carrier interactions are studied in natural bilayer MoTe2. Gate-dependent photoluminescence and reflectance spectroscopy reveal bright intralayer and interlayer excitonic resonances that can be tuned by an out-of-plane displacement field. The electric field modifies the layer character of the excitons through interlayer hybridization, establishing bilayer MoTe2 as a platform for studying layer-hybridized excitons and their many-body dressing by carriers. Upon electrostatic doping, these excitonic states evolve into multiple attractive and repulsive Fermi polaron branches. In particular, an interlayer Fermi polaron branch emerges when tunneling-mixed excitons are dressed by carriers in the opposite layer, demonstrating an additional many-body dressing channel enabled by the layer degree of freedom. Finally, correlated electronic behavior is investigated in MoTe2-based moiré heterostructures. Dual-gated MoSe2/MoTe2 heterobilayers exhibit resistance peaks near integer moiré fillings, consistent with signatures of correlated insulating behavior. However, contact resistance, gate instability, and limited displacement-field tunability prevent a definitive identification of a continuous Mott transition. Complementary optical measurements reveal gate-dependent excitonic evolution and charge redistribution, but no clear correlated optical anomaly within the accessible gate range. Together, these studies demonstrate how van der Waals heterostructures enable electrical, optical, and structural control of exciton–photon coupling, exciton–carrier interactions, and moiré-correlated electronic states.