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I. Growth of atomically uniform thin films and heterostructures by molecular beam epitaxy (MBE)

Nanoscale thin films, functional materials and artificial heterostructures can be exquisitely grown by MBE, a process in which atomic layers are sequentially deposited epitaxially onto a pre-treated substrate in an ultra-high-vacuum (UHV) chamber. Much potential is offered by MBE techniques for research based on precise fabrication of low dimensional materials. We seek to fabricate varous topological/functional thin films and heterostructures with a precision up to a single atomic layer by using our MBE facilities. This is exciting for fundamental physics due to the great flexibility in material engineering. 

II. Photoemission characterization and first-principles modeling of low-dimensional quantum systems

Angle-resolved photoemission spectroscopy (ARPES) is a powerful tool to visualize the electronic band structure of solid-state materials. We are setting up an ultrahigh resolution angle-resolved photoemission system (with a connection to MBE) to achieve in-situ characterizations of MBE-grown quantum materials. We also perform theoretical modeling and first-principles simulations to explain ARPES spectra taken from the artificial 2D systems. With the aid of density-functional-theory (DFT) packages such as VASP, ABINIT and QUANTUM ESPRESSO, we can establish a comprehensive understanding of electronic structure, spin texture, Berry phases (topological charges), and electron correlation effects of low-dimensional materials. 

III. Search, design and synthesis of new topological phases of condensed matter

Ever since the discovery of topological insulators, there have been emerging worldwide intense research activities in searching and identifying new topological phases of condensed matter. Recent years have witnessed the laboratory-based realization of numerous new topological matters such as topological Kondo insulators, topological crystalline insulator, topological superconductors, Dirac semimetals, Weyl semimetals, and topological nodal-line semimetals. The interest in this topic is from not only the realization of exotic theoretical concepts in fundamental physics but also a huge promise of device applications which could potentially revolutionize the entire Si-based electronics industry. We employ a methodology combining DFT, MBE and ARPES to search, synthesize and characterize novel topological condensed matters.