近日，美国波士顿学院的Qiong Ma及其研究小组与哈佛大学的Su-Yang Xu以及新加坡南洋理工大学的Guoqing Chang等人合作并取得一项新进展。经过不懈努力，他们发现TaIrTe₄中密度调谐关联的双量子自旋霍尔绝缘体。相关研究成果已于2024年3月20日在国际权威学术期刊《自然》上发表。

该研究团队报道了TaIrTe₄单层晶体中的新颖双QSH绝缘体现象，这源于其独特的单粒子拓扑结构和电子关联密度的相互作用。在电荷中性条件下，单层TaIrTe4展现出QSH绝缘体的特性，具有显著的非局部输运能力和量子化的螺旋边缘电导。当引入电子后，TaIrTe₄在极小的电荷密度范围内短暂表现为金属行为，但随后迅速进入新的绝缘状态，这一转变完全超出了基于其单粒子带结构的预期。这种绝缘状态很可能是范霍夫奇点附近强烈的电子不稳定性导致的，可能伴随着电荷密度波(CDW)的形成。

值得注意的是，在这个关联的绝缘能隙内，研究人员观察到QSH态的复苏。在CDW能隙中观察螺旋边缘传导可以架起自旋物理和电荷序的桥梁。双QSH绝缘子的发现引入了一种通过CDW超晶格创建拓扑平面微带的新方法，为探索时间反演对称分数相和电磁学提供了一个有前途的平台。

据悉，拓扑与关联性的收敛成为探寻物质新量子态的诱人领域。在量子自旋霍尔（QSH）绝缘体中引入电子关联性，能够催生分数拓扑绝缘体等奇特现象，以及时间反演对称拓扑序的出现，这在量子霍尔和陈绝缘体系统中是前所未见的。

附：英文原文

Title: Dual quantum spin Hall insulator by density-tuned correlations in TaIrTe₄

Author: Tang, Jian, Ding, Thomas Siyuan, Chen, Hongyu, Gao, Anyuan, Qian, Tiema, Huang, Zumeng, Sun, Zhe, Han, Xin, Strasser, Alex, Li, Jiangxu, Geiwitz, Michael, Shehabeldin, Mohamed, Belosevich, Vsevolod, Wang, Zihan, Wang, Yiping, Watanabe, Kenji, Taniguchi, Takashi, Bell, David C., Wang, Ziqiang, Fu, Liang, Zhang, Yang, Qian, Xiaofeng, Burch, Kenneth S., Shi, Youguo, Ni, Ni, Chang, Guoqing, Xu, Su-Yang, Ma, Qiong

Issue&Volume: 2024-03-20

Abstract: The convergence of topology and correlations represents a highly coveted realm in the pursuit of new quantum states of matter. Introducing electron correlations to a quantum spin Hall (QSH) insulator can lead to the emergence of a fractional topological insulator and other exotic time-reversal-symmetric topological order, not possible in quantum Hall and Chern insulator systems. Here we report a new dual QSH insulator within the intrinsic monolayer crystal of TaIrTe₄, arising from the interplay of its single-particle topology and density-tuned electron correlations. At charge neutrality, monolayer TaIrTe₄ demonstrates the QSH insulator, manifesting enhanced nonlocal transport and quantized helical edge conductance. After introducing electrons from charge neutrality, TaIrTe₄ shows metallic behaviour in only a small range of charge densities but quickly goes into a new insulating state, entirely unexpected on the basis of the single-particle band structure of TaIrTe₄. This insulating state could arise from a strong electronic instability near the van Hove singularities, probably leading to a charge density wave (CDW). Remarkably, within this correlated insulating gap, we observe a resurgence of the QSH state. The observation of helical edge conduction in a CDW gap could bridge spin physics and charge orders. The discovery of a dual QSH insulator introduces a new method for creating topological flat minibands through CDW superlattices, which offer a promising platform for exploring time-reversal-symmetric fractional phases and electromagnetism.

DOI: 10.1038/s41586-024-07211-8

Source: https://www.nature.com/articles/s41586-024-07211-8