Abstract
This thesis investigates novel electronic transport phenomena in two-dimensional (2D) transition metal dichalcogenide (TMDC) devices. In the Introduction, the fundamental properties of two-dimensional materials are reviewed, with emphasis on the crystal and electronic structures of TMDCs, their layer-dependent bandgaps, spin-orbit coupling, valley physics, quantum transport, moiré superlattices, correlated insulating states and 2D ferroelectricity.
To explore these phenomena experimentally, high-quality hBN-encapsulated dual-gated devices were fabricated using mechanical exfoliation, polymer-free dry transfer with the tear-and-stack method, electron-beam lithography and optimized surface-contact strategies, followed by low-temperature four-probe magneto-transport measurements. In Chapter 3, systematic studies on five- and six-layer MoS2 devices revealed robust monolayer-like K-valley quantum transport, contrary to conventional expectations of Q-valley dominance. Shubnikov-de Haas oscillations exhibit a Landau-level degeneracy of exactly 2, interaction-enhanced valley Zeeman splitting with even-to-odd filling transitions and a second twofold-degenerate band corresponding to the upper spin-orbit-split subband within the same atomic layer.
Chapter 4 reports a pronounced correlation-enhanced resistance hysteresis in angle-aligned MoS2 /WSe2 moiré heterobilayers. This hysteresis is sharply pinned to the moiré half-filling correlated insulating state and quantitatively co-varies with the insulating gap across carrier density, displacement field and temperature. Control experiments rule out extrinsic mechanisms. The observations are consistent with a Hubbard-band model in which interfacial polarization hysteresis renormalizes the effective displacement field, thereby modulating the field-sensitive correlation gap near half-filling.
Collectively, these results uncover unexpected valley physics in multilayer MoS2 and correlation-driven hysteretic transport in TMDC moiré systems, advancing the fundamental understanding of tunable many-body states in 2D materials and laying the foundation for future functional van der Waals devices.