Possible Topological States in Various Two-dimensional Systems

Jung-Jung Su^1*, Yung-Chun Chao¹, Pin-Jui Hsu²

¹Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
²Department of Physics, National Tsing Hua University, Hsinchu, Taiwan

* Presenter:Jung-Jung Su, email:jungjsu@nycu.edu.tw

Topological insulator (TI) has been intensively studied in the recent decades. In this class of topological material, the topological properties are protected by time-reversal symmetry. Even more exotically, physicists now introduce magnetic order to TI that breaks
the time-reversal while giving rise to a new type of order. This new class of topological material is generally referred to as the magnetic topological insulators (MTIs). MTIs posses finite Chern numbers and exhibits finite and quantized Hall
conductance even under zero external magnetic field, known as the quantum anomalous Hall (QAH) effect. This effect has been proposed to have potential applications in dissipationless electronic transport. However, an efficient process of introducing magnetic element to TI to produce MTI is still unclear.

We study various two-dimensional layered material, ferromagnetic or not, on top of three-dimensional topological related substrate. That includes the 2D topologically non-trivial stanene on few-layer cobalt (ferromagnetic) on Cu(111), and most recently, hexagonal FeTe monolayer on 3D topological insulator of Bi2Te3. In this FeTe/BT system, lattice constant, Moiré periodicity, and density of state have been determined by
scanning tunneling microscopic techniques. Along side with that, we perform density functional theory (DFT) calculation. The relaxed structure and the density of state result shows consistency with the STM measurement.

I will also discuss our latest fractional quantum Hall calculation in twisted bilayer of transition metal dichalcogenide (TMD) if times allows.

Keywords: two-dimensional, van der Waal material, quantum Hall effect, magnetic topological insulator