Transition metal dichalcogenides possess a unique combination of properties that make them a malleable platform to study and engineer light-matter interactions. On one hand, monolayers of WS2 naturally occur in the semiconducting 1H phase whose optical properties are dominated by excitons emerging from the band edges at the K valley. On the other hand, the 1T phase exhibits metallic properties and can be triggered by weak external stimuli. Here we use plasma irradiation to engineer a 1H/1T mixed phase state in WS2 and control the grain size of the 1T patches by tuning the irradiation time. We show that in the mixed phase WS2 a band nesting effect gives rise to new critical points resulting in a low-energy excitonic transition below the A exciton. Compared to standard excitons in WS2, this new resonance shows larger absorption and longer lifetime. The combination of these properties suggests new concepts for exciton-based optoelectronic devices that could stem from the control of phase mixture states in two-dimensional semiconductors.

中文翻译：

---

具有1H/1T相混合物的单层WS2中低能激子态的出现

过渡金属二硫属化物具有独特的特性组合，使其成为研究和设计光物质相互作用的可延展平台。一方面，WS2 的单层自然存在于半导体 1H 相中，其光学特性主要由从 K 谷带边缘出现的激子控制。另一方面，1T 相表现出金属特性，可以被微弱的外部刺激触发。在这里，我们使用等离子体辐照来设计 WS2 中的 1H/1T 混合相态，并通过调整辐照时间来控制 1T 贴片的晶粒尺寸。我们表明，在混合相 WS2 中，带嵌套效应产生了新的临界点，导致低于 A 激子的低能激子跃迁。与 WS2 中的标准激子相比，这种新的共振显示出更大的吸收和更长的寿命。