Prof. Lexian Yang

Tsinghua University, China

Speech Title: Evolution of the electronic structure of intrinsic magnetic topological insulator MnBi₂Te₄ film and bulk

Abstract: 

Intrinsic magnetic topological insulator MnBi2Te4, after been exfoliated to atomically thin film and electrostatically gated, exhibits rich and fascinating quantum properties such as quantum anomalous Hall effect and axion insulator state. However, despite these great breakthroughs, there are still many mysteries in the electronic structure of MnBi2Te4 to be understood. First of all, the topological surface states (TSSs) were observed by angle-resolved photoemission spectroscopy (ARPES) only at low photon-energies and exhibit a diminishing energy gap that is immune to the magnetic transition, in drastic contrast to the theoretical prediction and transport measurements. Secondly, the dispersion of TSSs shows a kink-like structure and is strongly broadened near the Fermi level (EF), which is out of the expectation of Fermi liquid theory. Thirdly and also importantly, although the intriguing transport properties are realized in MnBi2Te4 thin films, their electronic structure is not sufficiently investigated by experiments and seems to be in drastic contrast to that of bulk material. In this talk, we will show our ARPES studies on the electronic structure of MnBi2Te4 film and bulk material as well as their evolution with temperature, film thickness, and surface doping of alkali metals. We will also discuss the contradiction between ARPES experiment and transport measurements. 

Biography

Lexian Yang received his B.S. and Ph.D degrees from Fudan University in China, and then continued his research career as a Humboldt researcher in Kiel University, Germany. He has been an associate professor at the department of physics, Tsinghua University, China since 2019. His research interest focuses on the investigation of the electronic structures and novel properties of quantum materials using angle-resolved photoemission spectroscopy (ARPES), including the topological quantum materials, strongly correlated materials, low-dimensional materials, and advanced functional materials. He is also interested in developing advanced ARPES instruments with multiple detection capabilities such as spin, time, and spatial resolutions.