The discovery of correlated insulating, superconducting, and topological states found in twisted bilayer graphene systems suggests that two-dimensional (2D) moiré superlattices are new platforms to study the correlation effects. Similar to graphene, Transitional metal dichalcogenides (TMDCs) are layered 2D semi[1]conductors that allow the fabrication of van der Waals (vdW) heterostructures and the study of the correlation effects. This thesis describes the unconventional electronic transport in TMDCs moiré superlattices, espe[1]cially the unconventional ferroelectricity in MoS2/WSe2 heterobilayers.

In the first step, the investigation of unconventional physical properties of TMDCs through transport measurement depends on the contact performance with metals. The electrical contact between atomically thin TMDCs and metal leads is challenging due to the undesired interface barriers. We demonstrate a strategy to reduce the barrier and increase the carrier-injection efficiency by locally distorting the chemical bonds of TMDCs at the interface. The precisely controlled plasma treatment can generate a transition of TMDCs from a semiconducting 2H phase to a semimetallic 1T phase at the interface. The locally generated 1T TMDCs can bridge the gap between TMDCs and metal leads. The performance improvements are reflected by the low contact resistance and high carrier mobilities. We then applied this strategy to achieve ohmic contacts on TMDCs heterostructures at cryogenic temperatures and probe the unconventional physical properties through transport measurements.

Through stacking engineering, the stacking order and twist angle between the layers of TMDCs can be controlled to create the interface with broken inversion symmetry and electronic polarization, giving rise to the recently discovered ferroelectric polarizations in several heterostructures, including parallel-stacked bo[1]ron nitride (BN) and TMDCs. We demonstrate the unconventional ferroelectricity near the half-filling state of antiparallel-stacked double-bilayer WSe2 and MoS2/WSe2 heterobilayers. The emergence of ferroelectric[1]ity in these systems is unconventional and cannot be explained by the atomic structure model but by a theo[1]retical picture that features the correlation-induced layer-specific polarization and interlayer charge transfer based on the Hubbard model.