学术报告：拓扑半金属表面态量子输运研究

报告人：张成 研究员（复旦大学微纳电子器件与量子计算机研究院）

邀请人：苗霖 教授

报告时间： 2022年6月24日（周五）   上午10：00-11：00

腾讯会议：623-680-124

摘要：

Owing to the coupling between open Fermi arcs on opposite surfaces, topological semimetals exhibit a new type of cyclotron orbit in the surface states known as Weyl orbit. The overall Weyl orbit consists of two half-cycles in the momentum space and two propagating parts in the real space. It differs from conventional cyclotron orbits owing to the additional bulk propagating process along the magnetic field direction through the chiral modes of Weyl fermions. In this talk, I will discuss the quantum transport properties of Fermi arc surface states in Cd₃As₂ and NbAs, and show how they are related to the Weyl physics [1]. In Cd₃As₂, the relation between Fermi level and Fermi surface size of Weyl orbit is investigated. More interestingly, this semiclassical Weyl orbit is further found to exhibit quantum Hall effect in high magnetic fields [2-3]. We study the thickness dependence of oscillation phase factor to reveal the 3D feature in this Weyl-orbit-based quantum Hall effect. In contrast, the surface states in NbAs exhibit high-frequency quantum oscillations even when the Fermi level is near the Weyl nodes, resulting in exceptionally high electrical conductivity far away from the quantized value [4]. The origin for such distinction between these two systems will be discussed.

参考文献：

[1] C. Zhang et al. Nature Reviews Physics 3, 660-670 (2021)

[2] C. Zhang et al. Nature 565, 331–336 (2019).

[3] C. Zhang et al. Nature Communications 8, 1272 (2017)

[4] C. Zhang et al. Nature Materials 18, 482-488 (2019).

简历：张成，2014年和2019年分别获复旦大学物理系学士和博士学位，2017至2018年在华盛顿大学物理系任访问学者，2019年加入复旦大学微纳电子器件与量子计算机研究院担任青年研究员、博士生导师，入选国家万人计划青年拔尖人才、上海市青年拔尖人才和上海市青年科技英才扬帆计划等人才项目。主要从事拓扑电子态的量子输运、量子调控和拓扑电子器件研究，代表性工作包括发现基于外尔轨道的三维量子霍尔效应；发现准线性费米弧表面态的低耗散特性并实现二维体系最高面电导率；利用非局域输运方案实现外尔费米子的手性极化操控；利用红外磁光谱首次发现动态手性反常等。在Nature、Nature Materials、Nature Communications等学术期刊共发表论文30余篇，总引用2200余次。