National Laboratory of Solid State Microstructures &Department of Materials Science and Engineering, Nanjing University, Nanjing 210093 China.
National Laboratory of Solid State Microstructures &Department of Physics, Nanjing University, Nanjing 210093 China.
Sci Rep. 2017 Mar 15;7:44587. doi: 10.1038/srep44587.
Transition metal dichalcogenides (TMDs) WTe and MoTe with orthorhombic Td phase, being potential candidates as type-II Weyl semimetals, are attracted much attention recently. Here we synthesized a series of miscible MoWTe single crystals by bromine vapor transport method. Composition-dependent X-ray diffraction and Raman spectroscopy, as well as composition and temperature-dependent resistivity prove that the tunable crystal structure (from hexagonal (2H), monoclinic (β) to orthorhombic (Td) phase) can be realized by increasing W content in MoWTe. Simultaneously the electrical property gradually evolves from semiconductor to semimetal behavior. Temperature-dependent Raman spectroscopy proves that temperature also can induce the structural phase transition from β to Td phase in MoWTe crystals. Based on aforementioned characterizations, we map out the temperature and composition dependent phase diagram of MoWTe system. In addition, a series of electrical parameters, such as carrier type, carrier concentration and mobility, have also been presented. This work offers a scheme to accurately control structural phase in MoWTe system, which can be used to explore type-II Weyl semimetal, as well as temperature/composition controlled topological phase transition therein.
过渡金属二卤化物 (TMD) WTe 和 MoTe 具有正交 Td 相，作为潜在的 II 型外尔半金属，最近受到了广泛关注。在这里，我们通过溴蒸气输运法合成了一系列混溶性 MoWTe 单晶。成分依赖的 X 射线衍射和拉曼光谱以及成分和温度依赖的电阻率证明，通过增加 MoWTe 中的 W 含量可以实现可调谐的晶体结构（从六方 (2H)、单斜 (β) 到正交 (Td) 相）。同时，电性能也逐渐从半导体演变为金属行为。温度依赖的拉曼光谱证明，温度也可以在 MoWTe 晶体中诱导从β到 Td 相的结构相变。基于上述表征，我们绘制了 MoWTe 体系的温度和成分相关相图。此外，还提出了一系列电参数，如载流子类型、载流子浓度和迁移率等。这项工作提供了一种在 MoWTe 体系中精确控制结构相的方案，可用于探索 II 型外尔半金属以及其中的温度/成分控制拓扑相变。
