Graphene is a single layer of carbon atoms with a two-dimensional honeycomb lattice. Transition metal dichalcogenide (TMD or TMDC) are also honeycomb lattice. They are atomically thin semiconductors of the type MX₂, with M a transition metal atom (Mo, W, etc.) and X a chalcogen atom (S, Se, or Te). In each single layer MX₂, one layer of M atoms is sandwiched between two layers of X atoms. The electron transport in these atomically thin two-dimensional materials usually behaves quite differently from their bulk. This dissertation mainly discusses the fabrication and transport properties of atomically thin graphite and WSe₂, with a focus on the quantum transport behavior, including the Shubnikov–de Haas oscillations, flat bands and electron interaction behaviors.

Achieving Ohmic contact...[ Read more ]

Graphene is a single layer of carbon atoms with a two-dimensional honeycomb lattice. Transition metal dichalcogenide (TMD or TMDC) are also honeycomb lattice. They are atomically thin semiconductors of the type MX₂, with M a transition metal atom (Mo, W, etc.) and X a chalcogen atom (S, Se, or Te). In each single layer MX₂, one layer of M atoms is sandwiched between two layers of X atoms. The electron transport in these atomically thin two-dimensional materials usually behaves quite differently from their bulk. This dissertation mainly discusses the fabrication and transport properties of atomically thin graphite and WSe₂, with a focus on the quantum transport behavior, including the Shubnikov–de Haas oscillations, flat bands and electron interaction behaviors.

Achieving Ohmic contact and avoiding possible contamination is the key to probe the intrinsic electronic properties and correlation electron effects for atomically thin graphite and WSe₂. By combing selective etching and bottom electrode method, high quality trilayer graphene and few layer WSe₂ field effect transistors have been fabricated. For WSe₂, enhanced electron-electron interactions effects have been observed result from the reduced screening in two-dimensional limits and large Wigner-Seitz radius. We experimentally demonstrate strong Coulomb interaction effects in quantum Hall regime of few-layer WSe₂ through its quantum transport behavior in tilted magnetic fields.

Twisted bilayer graphene provides another two-dimensional platform for studying electron interaction phenomena and flat band properties such as correlated insulator transition, superconductivity and ferromagnetism at 1.1° magic angles. Here, we present experimental characterization of interaction effects and superconductivity signatures in p-type twisted double-bilayer WSe₂. Enhanced interlayer interactions are observed when the twist angle decreases to a few degrees as reflected by the high-order satellites in the electron diffraction patterns taken from the reconstructed domains from a conventional moiré superlattice. In contrast to twisted bilayer graphene, there is no specific magic angle for twisted WSe₂. Flat band properties are observable at twist angles ranging from 1 to 4 degrees. In the final, by stacking two flakes of few layers WSe₂ with a small rotation angle, we generate a new type of atomically thin crystalline system for investigating the Moiré bands and their quantum oscillations under high magnetic fields.