Realization of Multiple Charge-Density Waves in NbTe<sub>2</sub> at the Monolayer Limit
Yusong Bai, Tao Jian, Zemin Pan, Jinghao Deng, Xiaoyu Lin, Chao Zhu, Da Huo, Zhengbo Cheng, Yong Liu, Ping Cui, Zhenyu Zhang, Qiang Zou, Chendong Zhang
Abstract
Layered transition-metal dichalcogenides down to the monolayer (ML) limit provide a fertile platform for exploring charge-density waves (CDWs). Here, we experimentally unveil the richness of the CDW phases in ML-NbTe 2 for the first time. Not only the theoretically predicted 4 × 4 and 4 × 1 phases but also two unexpected 28 × 28 and 19 × 19 phases are realized. For such a complex CDW system, we establish an exhaustive growth phase diagram via systematic efforts in the material synthesis and scanning tunneling microscope characterization. Moreover, the energetically stable phase is the larger-scale order ( 19 × 19 ), which is surprisingly in contradiction to the prior prediction (4 × 4). These findings are confirmed using two different kinetic pathways: i.e., direct growth at proper growth temperatures ( T ) and low- T growth followed by high- T annealing. Our results provide a comprehensive diagram of the “zoo” of CDW orders in ML-NbTe 2 .