近日，美国普林斯顿大学的M. Zahid Hasan&Md Shafayat Hossain及其研究小组与英国伦敦帝国理工学院的Frank Schindler等人合作并取得一项新进展。他们对单质固体中的混合拓扑量子态进行了研究。相关研究成果已于2024年4月10日在国际权威学术期刊《自然》上发表。

该研究团队通过结合隧道显微镜、光电发射光谱和理论分析，成功揭示了简单元素——固体砷中物质的“混合”拓扑相。他们发现，砷具有一种独特的体积-表面-边缘对应关系，这种关系稳定了混合拓扑相，并体现出结合强的高阶拓扑结构。尽管动量-空间光谱测量初步显示出拓扑表面状态的迹象，但实空间显微镜测量进一步揭示了砷表面上各种天然纳米结构上，拓扑诱导的阶梯边缘传导通道的独特几何形状。

通过理论模型的深入分析，研究人员证明，砷中无能隙阶跃边缘态的存在依赖于非平凡强Z₂不变量，和非平凡高阶拓扑不变量的同时存在，这为混合拓扑相的存在提供了确凿的实验证据。这项研究突出了在工程量子或纳米器件中，深入探索不同带拓扑之间相互作用的重要性，以及如何利用这些相互作用所带来的拓扑传导通道。

据悉，拓扑学和相互作用是现代量子物质研究中的基本观念。这两者之间的紧密联系催生了三个关键的研究方向：一是探讨不同相互作用之间的竞争关系，特别是在多个相互交织的相态中；二是研究相互作用与拓扑之间的交互如何驱动扭曲层状材料和拓扑磁体中的独特现象；三是探究多个拓扑序的合并如何孕育出各种新颖相态。前两个方向已经成为研究热点，而最后一个方向尽管尚未得到充分探索，主要是因为缺乏合适的实验材料平台。

附：英文原文

Title: A hybrid topological quantum state in an elemental solid

Author: Hossain, Md Shafayat, Schindler, Frank, Islam, Rajibul, Muhammad, Zahir, Jiang, Yu-Xiao, Cheng, Zi-Jia, Zhang, Qi, Hou, Tao, Chen, Hongyu, Litskevich, Maksim, Casas, Brian, Yin, Jia-Xin, Cochran, Tyler A., Yahyavi, Mohammad, Yang, Xian P., Balicas, Luis, Chang, Guoqing, Zhao, Weisheng, Neupert, Titus, Hasan, M. Zahid

Issue&Volume: 2024-04-10

Abstract: Topology and interactions are foundational concepts in the modern understanding of quantum matter. Their nexus yields three important research directions: (1) the competition between distinct interactions, as in several intertwined phases, (2) the interplay between interactions and topology that drives the phenomena in twisted layered materials and topological magnets, and (3) the coalescence of several topological orders to generate distinct novel phases. The first two examples have grown into major areas of research, although the last example remains mostly unexplored, mainly because of the lack of a material platform for experimental studies. Here, using tunnelling microscopy, photoemission spectroscopy and a theoretical analysis, we unveil a ‘hybrid’ topological phase of matter in the simple elemental-solid arsenic. Through a unique bulk-surface-edge correspondence, we uncover that arsenic features a conjoined strong and higher-order topology that stabilizes a hybrid topological phase. Although momentum-space spectroscopy measurements show signs of topological surface states, real-space microscopy measurements unravel a unique geometry of topologically induced step-edge conduction channels revealed on various natural nanostructures on the surface. Using theoretical models, we show that the existence of gapless step-edge states in arsenic relies on the simultaneous presence of both a non-trivial strong Z₂ invariant and a non-trivial higher-order topological invariant, which provide experimental evidence for hybrid topology. Our study highlights pathways for exploring the interplay of different band topologies and harnessing the associated topological conduction channels in engineered quantum or nano-devices.

DOI: 10.1038/s41586-024-07203-8

Source: https://www.nature.com/articles/s41586-024-07203-8