报告人：张远波 教授
主持人：孙政 研究员
时间：2021年10月29日（周五）上午10：00-12：00
地点：光学大楼B325会议室
报告人简介：
张远波教授，2000年获北京大学学士学位。2000年8月赴美国哥伦比亚大学物理系，于2006年获博士学位。同年获美国加州大学伯克利分校为期三年的Miller Fellowship，从事博士后研究。2011年起为复旦特聘教授，博士生导师。张远波教授的研究方向为低维纳米体系，特别是石墨烯的电学和光学研究。在量子输运，扫描隧道显微和能谱领域积累了一定的研究经验。2015年获得基金委杰出青年基金。另外还获得腾讯科学探索奖（2020），“求是”杰出青年学者奖（2013），上海市东方学者（2012），IUPAP Young Scientist Prize (IUPAP, 2010), Charles H. Townes Fellowship（Columbia University, 2005），Miller Fellowship Award（UC Berkeley，2006）等奖项。
报告内容：
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 area for further exploring various topological phenomena.