Li Bo, Wang Jing, Wu Qilong, Tian Qiwei, Li Ping, Zhang Li, Yin Long-Jing, Tian Yuan, Johnny Wong Ping Kwan, Qin Zhihui, Zhang Lijie
Key Laboratory for Micro/Nano Optoelectronic Devices of Ministry of Education & Hunan Provincial Key Laboratory of Low-Dimensional Structural Physics and Devices, School of Physics and Electronics, Hunan University, Changsha 410082, People's Republic of China.
State Key Laboratory for Mechanical Behavior of Materials, Center for Spintronics and Quantum Systems, School of Materials Science and Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, People's Republic of China.
ACS Appl Mater Interfaces. 2022 Jul 20;14(28):32738-32746. doi: 10.1021/acsami.2c08397. Epub 2022 Jul 8.
Monolayer PbSe has been predicted to be a two-dimensional (2D) topological crystalline insulator (TCI) with crystalline symmetry-protected Dirac-cone-like edge states. Recently, few-layered epitaxial PbSe has been grown on the SrTiO substrate successfully, but the corresponding signature of the TCI was only observed for films not thinner than seven monolayers, largely due to interfacial strain. Here, we demonstrate a two-step method based on molecular beam epitaxy for the growth of the PbSe-CuSe lateral heterostructure on the Cu(111) substrate, in which we observe a nanopore-patterned CuSe layer that acts as the template for lateral epitaxial growth of PbSe. This further results in a PbSe-CuSe lateral heterostructure with an atomically sharp interface. Scanning tunneling microscopy and spectroscopy measurements reveal a fourfold symmetric square lattice of such PbSe with a quasi-particle band gap of 1.8 eV, a value highly comparable with the theoretical value of freestanding PbSe. The weak monolayer-substrate interaction is further supported by both density functional theory (DFT) and projected crystal orbital Hamilton population, with the former predicting the monolayer's anti-bond state to reside below the Fermi level. Our work demonstrates a practical strategy to fabricate a high-quality in-plane heterostructure, involving a monolayer TCI, which is viable for further exploration of the topology-derived quantum physics and phenomena in the monolayer limit.
单层PbSe被预测为一种二维（2D）拓扑晶体绝缘体（TCI），具有晶体对称性保护的类狄拉克锥边缘态。最近，已成功在SrTiO衬底上生长出少层外延PbSe，但仅在不薄于七个单层的薄膜中观察到TCI的相应特征，这主要归因于界面应变。在此，我们展示了一种基于分子束外延的两步法，用于在Cu(111)衬底上生长PbSe-CuSe横向异质结构，其中我们观察到一个纳米孔图案化的CuSe层，它作为PbSe横向外延生长的模板。这进一步形成了具有原子级尖锐界面的PbSe-CuSe横向异质结构。扫描隧道显微镜和光谱测量揭示了这种PbSe的四重对称方形晶格，其准粒子带隙为1.8 eV，该值与独立PbSe的理论值高度可比。密度泛函理论（DFT）和投影晶体轨道哈密顿布居均进一步支持了单层与衬底之间的弱相互作用，前者预测单层的反键态位于费米能级以下。我们的工作展示了一种制造高质量平面异质结构的实用策略，该结构涉及单层TCI，对于在单层极限下进一步探索拓扑衍生的量子物理和现象是可行的。
