School of Physical Science and Technology (SPST) Professor Chen Yulin’s group recently published a review article on the photoemission study of quantum materials in Nature Reviews Materials titled ‘Visualizing electronic structures of quantum materials by angle-resolved photoemission spectroscopy.’
Electronic structures are the genes of materials that determine their electronic, magnetic, optical properties and relevant applications. Capable of directly visualizing the band dispersions and Fermi surface topography, angle-resolved photoemission spectroscopy (ARPES) has emerged as a powerful experimental tool to investigate electronic structures and their coupling to different degrees of freedom in materials.
Among the vast number of new materials, topological quantum materials (TQMs) represent a brand-new class of quantum matter that can be characterized by topological invariant, and have recently attracted significant research attention. Since the discovery of the quantum Hall effect in 1980 and the recent prediction and realization of quantum Spin Hall effect in 2005, great efforts have been devoted to the investigation of different exotic topological phases in solids, such as topological insulators, topological Dirac and Weyl semimetals, topological superconductors, etc. Among these efforts, ARPES has provided the most straightforward experimental proof revealing the existence of these new topological phases.
Meanwhile, the study on 2D transitional metal chalcogenides (TMDs) is another timely topic for condensed matter physics and material science due to their rich and tunable properties (e.g. thickness-dependent indirect-direct crossover of bandgap, superconductivity, charge density wave, and the quantum Spin Hall effect, etc.) with great application potential in electronic and spintronic devices. In the study of these functional materials, ARPES has also played a key role in the past decade, especially with the development of spatially resolved ARPES technique (i.e. micro- and nano-ARPES) allowing us to directly study the low dimensional TMDs with mesoscopic size or in devices.
The review article first introduced the principle of the ARPES (see Figure 1), then gave a demonstration in the studies on TQMs and TMDs with a focus on the direct relation between its novel physical properties and the electronic structure. Finally, the review outlined future development of ARPES and its great potential in condensed matter physics and materials sciences.
Professor Chen Yulin’s group is a leading ARPES group focusing their research on discovering and investigating novel states of quantum matter. Their endeavor has led to fruitful results and publications in renowned scientific journals (see Figure 2), including the discoveries/investigations of massless/massive 2D Dirac fermions in 3D topological insulators; 3D Dirac fermions (in 3D Dirac semimetals) and Weyl fermions (in Weyl semimetals with Fermi arcs); as well as other exotic topological phases such as nodal-line semimetals and hourglass fermions. Furthermore, with the support of SPST, Chen’s group is also devoted to the development of advanced scientific facilities, based on the infrastructure of advanced light sources in Shanghai, including the Shanghai Synchrotron Radiation Facility and the high frequency X-ray free electron laser currently under construction.
The review paper mainly focuses on a series of important works in the field of TQMs and TMDs from Professor Chen’s group and many other groups. The credit of the article also includes Dr. Yang Haifeng as first author and other ShanghaiTech academics, who were jointly supported by the National Science Foundation of China, the Shanghai Municipal Science and Technology Commission, ShanghaiTech University and China Postdoctoral Science Foundation.
Read more at: https://doi.org/10.1038/s41578-018-0047-2
Figure 1：a. The principle of angle-resolved photoemission spectroscopy (ARPES) measurement. b. Simulated ARPES data showing the band structure of a 2D free-electron system. c. An illustration of an ARPES spectrometer.
Figure 2：Electronic structure of quantum materials probed by ARPES. a. Topological insulator (Bi2Te3). b. Massless Dirac fermion (Na3Bi). c. Weyl fermions with surface Fermi arcs (TaAs). d. Transitional metal chalcogenide (MoS2).