CityU
Department of Physics
香港城市大學
City University of Hong Kong
Angle Resolved Photoemission Spectroscopy
Topological physics
We focus on the research of topological insulator (TI), topological semimetal, axion insulator, topological superconductor, etc., such as strong/weak TI, magnetic Dirac/Weyl semimetal, magnetic TI, unconventional TI, topological superconductivity on surface states, etc. In our previous studies, we have discovered the first hourglass fermion, Fermi arc of triple point fermion, Magnetic Weyl fermion by spin fluctuation, non-trivial magnetic Dirac fermion. We also aim to search for new kinds of quasi-fermions in crystals.
Superconductors
We study the electronic structure of new kinds of superconductors (SC) especially magnetic SC and coexistence of topology and superconductivity. With ARPES we can get the band structure, Fermi surface, SC gap and its symmetry, etc. ARPES provides an direct deep insight into the micro mechanism of superconductivity and plays an important role in the research of high temperature SC.
Correlation effect
Searching for new quantum phenomena induced by electron-boson coupling in condensed matter using ARPES will extend our understanding about the solids, which will also improve the development of device with new materials. For example, the correlation between electrons or electrons and bosons, and the (quantized) excitations of certain type of collective motion can lead to the emergence of various macroscopic quantum phenomena such as SC, charge/spin density wave, polarons, excitons, trions, etc. Exploring the rich quantum phenomena induced by electron-boson coupling in condensed matter has been a dynamic research front in the last decade and is still expected to make further progress.
Featured Research
Mobile excitons discovered in quasi-one-dimensional metal TaSe3
Charge neutrality and an expected itinerant nature makes excitons potential transmitters of information. Mobile excitons in metals have been elusive, as screening usually suppresses their formation. Very recently, using angle-resolved photoemission spectroscopy, we detect dispersing excitons for the first time in quasi-one-dimensional metallic trichalcogenide TaSe3.
Media Publicity
CityU Reports: 首次在金属中发现快速移动的激子，造就未来更高速数码通讯
Observation of Unpaired Singular Weyl Points Beyond Nielsen-Ninomiya No-go Theorem
All so-far experimentally determined Weyl semimetals (WSMs) have featured Weyl points that appear in pairs in the momentum space. Now, our research show that the WSM platinum gallium PtGa features a singular, unpaired Weyl point surrounded by closed Weyl nodal walls (WNW). This is the first time that an unpaired electronic WP has been observed experimentally and the first time that electronic topological WNWs/surfaces have been experimentally reported in crystalline solids.
Nature Communications volume 12, Article number: 3994 (2021)
Media Publicity
CityU news: CityU scientist hunted down the first unpaired Weyl magnetic monopole.
Phys.org news: Physicist observes the first unpaired Weyl magnetic monopole.
Magnetic Weyl fermions induced by spin Fluctuation
Discovering a new kind of magnetic Weyl semimetal induced by spin fluctuations.
Science. Adv. 5, eaaw4718 (2019).
Media Publicity
Observation of surface Fermi arcs of topological triple point semimetal
Triple point or three component Fermion is one new unconventional Fermion that between the degeneracy of Dirac Fermion and Weyl Fermion. Its topological nontrivial property is firstly proved by the surface Fermi arc observation.
Nature Physics 14, 349–354 (2018)
Nature 546, 627-631(2017)
Media Publicity
Nature Physics, news and views: Threes company. Nature Physics, 14,329–330(2018).
Discovery of Hourglass Fermion!
Protected by Nonsymmorphic symmetry, the surface sates of topological insulator can form a special structure like an hourglass rather than normal Dirac cone. It is firstly proved by our ARPES experiments: Science. Adv. 3, e1602415 (2017).
Media Publicity
Nature Physics, research highlights: Top of the hour. Nature Physics, 13, page529(2017).
Revealing the correlation induced self-doping effect in Fe-based superconductor Ba2Ti2Fe2As4O.
Doping effect plays an important role in the formation of superconductivity of high temperature SC. In this work, we proved for the first time that when we alternatively stack two non-SC parent compounds together, the charge transferring between them drives the system in to superconductivity.