磁性拓扑绝缘体中的新奇量子态

Searching for new states of quantum matter is the key part in condensed matter physics. The spin-orbit coupling, spin exchange coupling and correlation, and superconducting pairing in solids will give rise to many novel quantum states. Magnetic topological insulators can realize the quantum anomalous Hall effect where electrons on the edge can conduct without dissipation. Together with s-wave superconducting proximity coupling, the chiral topological superconducting state can be realized, where it hosts gapless chiral Majorana quasiparticle edge states. In the past few years, the quantum anomalous Hall effect has been realized in magnetic topological insulators experimentally. Most recently, the proximity coupling between magnetic topological insulators and s-wave superconductors has been realized, where the signature of chiral topological superconducting state is observed. This program aims to discover new organizational principles of electronic states associated with the spin degree of freedom, and develop new theoretical concepts. Taking magnetic topological insulators as an example, we will focus on investigating novel quantum states and novel phenomena arising from spin-orbit coupling, magnetic exchange interactions and superconducting pairing in solids. The research topics include transport properties of chiral topological superconducting state, scaling theory of topological superconducting phase transition, and magnetization dynamics of magnetic topological insulators, the interplay and relation between magnetism and band topology, new quantum states in coupled systems with ferromagnetism, anti-ferromagnetism, topology and superconducting pairing, designing and predicting materials with tailored functionality.

寻找新量子物态是凝聚态物理研究的热点。在固体中，自旋轨道耦合，自旋交换相互作用和关联，以及超导配对会导致许多新奇量子态。磁性拓扑绝缘体能够实现量子反常霍尔效应，存在边界无耗散的电子输运。与s-波超导体近邻效应将实现手征拓扑超导态，存在手征Majorana准粒子边界态。最近几年，量子反常霍尔效应被实验证实。最近，磁性拓扑绝缘体和超导近邻效应取得进展，并探测到手征拓扑超导态的迹象，将会激发一系列在磁性拓扑绝缘体中的实验和理论研究。本申请书旨在发现与自旋相关的新电子态的机制并发展新的理论概念。以磁性拓扑绝缘体为例，重点研究固体中自旋-轨道耦合、磁交换相互作用以及超导配对所导致的新量子态和物理现象。包括手征拓扑超导态的电、热以及热电输运性质，拓扑超导相变的标度理论，磁性拓扑绝缘体中的磁性动力学，磁性和拓扑能带的相互关系，寻找在铁磁、反铁磁、超导和拓扑耦合体系中的新量子态，以及设计和预言新的材料等。

发现新的拓扑物态和无耗散输运机制是凝聚态物理最重要的主题之一。对称性和拓扑之间的相互作用给出了各种不同的拓扑物态，而拓扑物态的对称性破缺又进一步生成了许多不同的拓扑物态。例如时间反演对称拓扑物态与磁性和超导的结合可以产生许多新奇的拓扑现象。磁性拓扑物态不仅丰富了物质形态，同时也为电子器件应用提供了可能。量子反常霍尔效应首次在磁性掺杂的拓扑绝缘体中发现。本项目集中研究与发现磁性拓扑绝缘体中的新奇量子物态并发展新的理论概念。主要进行了以下两个方面的研究：（一）发现新的磁性拓扑现象，寻找本征磁性拓扑物质，设计新平台和方案实现拓扑磁电效应，量子反常霍尔效应，动力学轴子等。预言陈数Moiré平带体系，为分数化拓扑态等提供物理平台。（二）探索时间反演对称破缺拓扑超导态与手征马约拉纳费米子的物理实现、拓扑现象以及输运理论。以磁性拓扑绝缘体为主，拓展到其它拓扑量子物质。主要研究结果包括本征磁性拓扑绝缘体MnBi2Te4的预言，为研究拓扑态提供了新平台，预言奇数层薄膜呈现量子反常霍尔效应被证实；手征马约拉纳费米子的物理实现、拓扑现象和量子输运理论，方案被多个实验组采纳；转角双层MnBi2Te4中拓扑陈数Moiré平带；零平台态、轴子绝缘态、拓扑磁电效应、动力学轴子；二维拓扑绝缘物态的普适能带理论等。这些结果加深了人们对凝聚态材料中新的拓扑现象和对称性破缺拓扑物态的新物理的理解。工作包括16篇文章，其中3篇PRL，1篇Science，1篇Nature，1篇Chinese Physics Letters，8篇PRB，1篇物理学报，1篇SPIN。