The convergence of topology and correlations represents a highly coveted realm in the pursuit of new quantum states of matter¹. 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^{2,3,4,5,6,7,8}, 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^2,3,4,9,10.

拓扑和相关性的融合代表了追求新的物质量子态的令人垂涎的领域¹。将电子关联引入量子自旋霍尔 (QSH) 绝缘体可以导致分数拓扑绝缘体和其他奇特的时间反转对称拓扑顺序^{2,3,4,5,6,7,8}的出现，这在量子中是不可能的霍尔和陈绝缘子系统。在这里，我们报告了 TaIrTe ₄固有单层晶体内的一种新的双 QSH 绝缘体，这是由其单粒子拓扑和密度调节电子相关性的相互作用产生的。在电荷中性时，单层 TaIrTe ₄表现出 QSH 绝缘体，表现出增强的非局域传输和量子化螺旋边缘电导。从电荷中性引入电子后，TaIrTe ₄仅在小范围的电荷密度下表现出金属行为，但很快进入新的绝缘状态，这在 TaIrTe ₄的单粒子能带结构的基础上完全出乎意料。这种绝缘状态可能是由范霍夫奇点附近强烈的电子不稳定性引起的，可能会导致电荷密度波（CDW）。值得注意的是，在这个相关的绝缘间隙内，我们观察到 QSH 状态的复苏。对 CDW 间隙中螺旋边缘传导的观察可以桥接自旋物理和电荷顺序。双 QSH 绝缘体的发现引入了一种通过 CDW 超晶格创建拓扑平坦微带的新方法，这为探索时间反转对称分数相和电磁学提供了一个有前景的平台^2,3,4,9,10。