- Lectures
- Institute of Physics
- Location
1F, Auditorium, Institute of Physics
- Speaker Name
Prof. Yuanbo Zhang (Department of Physics, Fudan University)
- State
Definitive
- Url
https://www.phys.sinica.edu.tw/lecture_detail.php?id=2758&eng=T
【Abstract】
In a magnetic topological insulator, nontrivial band topology conspires with magnetic order to produce exotic states of matter that are best exemplified by quantum anomalous Hall (QAH) insulators and axion insulators. Up till now, such magnetic topological insulators are obtained by doping topological insulators with magnetic atoms. The random magnetic dopants, however, inevitably introduce disorders that hinder further exploration of topological quantum effects in the material. We resolve this dilemma by probing quantum transport in MnBi2Te4 thin flake—a topological insulator with intrinsic magnetic order. In this layered van der Waals crystal, the ferromagnetic layers couple anti-parallel to each other, so bulk MnBi2Te4 is an antiferromagnet. Atomically thin MnBi2Te4, however, becomes ferromagnetic when the sample has odd number of septuple layers (a septuple layer represents a single structural unit in the out-of-plane direction). We observe zero-field QAH effect in a five-septuple-layer specimen; an external magnetic field further enhance the QAH quantization by forcing all layers to align ferromagnetically. MnBi2Te4 therefore becomes the first intrinsic magnetic topological insulator exhibiting QAH effect. The results establish MnBi2Te4 as an ideal arena for further exploring various topological phenomena.