Area of Excellence

Atomically thin 2D crystals and their van der Waals (vdW) heterostructures have proven their unprecedented potentials to reveal new quantum transport phenomena and ‘design’ various novel phases of matter, such as superconductivity, magnetism, topological phases, fractional quantum-Hall states, correlated insulating states, and so on, which will advance the modern solid-state physics at the forefront. By combining leading expertise of the team on electron transport, nanoscale quantum sensing, theoretical and advanced computational modelling, this task group will tackle coherently the properties and microscopic origins of the various exotic quantum phases in 2D materials, and explore the possibilities towards device applications and discovery of new quantum matters. To this end, we will concentrate our efforts on the two explorative themes: electron transport in quantum structures and quantum many-body phenomena.

This task group will work on two intertwined research themes in 2D semiconductors and their vdW heterostructures. The first is valley & spin physics. A trend for future electronics is to exploit electron’s quantum degree of freedom such as spin, in addition to the classical charge, as information carrier. Electrons in 2D crystals feature accessible quantum degrees of freedom, including valley (referring to inequivalent energy extrema in energy-momentum dispersion), and layer pseudospin carrying electric polarization. We will explore new physics associated with these quantum degrees of freedom in vdW heterostructures and the Moiré landscape, and various dynamic control possibilities that can allow their use as information carriers for future versatile electronics and optoelectronics. The second theme is light-matter interaction in two-dimension. Semiconducting 2D materials such as TMDs have attracted tremendous scientific and technological interests, for their appealing properties including the valley physics and the substantially enhanced Coulomb interaction in the reduced dimensionality. The latter results in strong excitonic effect that dominates the optical properties and light-matter interaction in 2D limit, leading to a new paradigm of optoelectronics and photonics based on excitons, the Coulomb bound electron-hole pair.

A key issue underlying 2D materials research is to realize various 2D crystals and quantum structures in high quality and large area. Two strategies, i.e., top-down and bottom-up, are currently adopted in parallel. The former is via exfoliation out of layered bulk crystals. A vast majority of current research rely on mechanically exfoliated flake samples which, however, are not scalable for future industry-level production. Liquid and chemical exfoliation methods offer the high-yield preparation of 2D materials but with relatively poor control over the size, thickness and crystal quality. Electrochemical intercalation and exfoliation method also provides a powerful tool to prepare high-quality 2D nanosheets in large scale. The bottom-up approaches of 2D materials growth include: chemical vapor deposition, pulse laser deposition, and molecular beam epitaxy techniques. The epitaxial growth methods offer a greater flexibility in achieving artificial quantum structures as well as in manipulating the growth characteristics such as the morphology, defects, and interfaces. This task group will broadly explore the various growth and synthesis approaches, aiming at high-quality 2D materials and heterostructures for subsequent property characterizations and device fabrications.

The varieties of 2D crystals feature a wide range of materials properties from metals, semi-metals to semiconductors and insulators. With the flexibility in assembling different 2D crystals by their vdW stacking, the elements needed for different types of devices can all be realized by atomically thin building blocks, which not only promise the ultimate miniaturization but also point to new geometries of devices. This task group will tackle critical issues for turning the appealing properties of 2D materials into functional devices, including: solving contacts, gate tunabilities, defect issues towards high quality device fabrications; new device geometries for flexible electronics and optoelectronics; efficient integration of different elements for practical valleytronics and spintronics.

The atomic thickness, remarkable structural stability and mechanical strength of 2D materials have promised their flexible hybridization with other physical systems, including plasmonic meta-materials, nano-fibers, low dimensional semiconductor structures such as nanodots and nanowires. Supported by other task groups, the aim of this group is to explore the integration of these exciting systems of distinct nature with 2D materials, thereby expanding their science and device applications.