Nanoscale Polymorph Engineering of Metal-Correlated Insulator Junctions in Monolayer NbSe<sub>2</sub>.

Chen, Yaoyao; Dai, Yi-Xin; Zhang, Yu; Zhang, Can; Zhou, Lili; Jia, Liangguang; Wang, Wei; Han, Xu et al. · ACS Nano · 2025

basic_science · Level V

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Abstract

Lateral junctions composed of quantum many-body materials are highly desirable for realizing physical phenomena and device concepts. However, controllable fabrication of high-quality junctions is challenging, which greatly hinders further exploration. Here, we successfully realize monolayer heterophase homojunctions of metallic H-NbSe<sub>2</sub> and correlated insulating T-NbSe<sub>2</sub> with atomically sharp boundaries via nanoscale polymorph engineering. By applying a scanning tunneling microscopy (STM) tip pulse, T-NbSe<sub>2</sub> can be locally introduced from H-NbSe<sub>2</sub> on the side beneath the tip, thus realizing H/T-NbSe<sub>2</sub> heterophase homojunctions. Our in situ STM measurements, complementary by the theoretical calculations, reveal two types of atomically sharp boundaries with distinct abilities for electron transmission, owing to the structure-dependent boundary coupling effects. Moreover, there are significant electronic interactions among the metallic, correlated insulating, and charge-density-wave states at the H/T-NbSe<sub>2</sub> boundaries. Our results provide insight into the interacting mechanism among diverse quantum many-body states.