Monolayer transition metal dichalcogenides (1L-TMDs) are excellent platforms for exciton physics. In tungsten-based 1L-TMDs, the existence of dark excitons at lower energy has important roles for bright exciton relaxation. However, the detailed relaxation dynamics from bright to dark excitons have not been revealed sufficiently. In this paper, we studied the rise dynamics of out-of-plane polarized photoluminescence (PL) from spin-forbidden dark excitons in monolayer WSe₂. Under conditions of resonant excitation to the bright 1s excitons, PL from the spin-forbidden dark exciton has a finite rise time of a few tens of picoseconds, which suggests that intermediate states, probably hot indirect dark excitons, should play an important role in the relaxation pathway from the bright to the spin-forbidden dark excitons. The excitation density dependence indicates that exciton–exciton scattering should promote faster relaxation to the spin-forbidden dark excitons.

中文翻译：

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暗激子态在单层 WSe2 中亮 1s 激子弛豫动力学中的作用

单层过渡金属二硫属化物 (1L-TMD) 是激子物理学的绝佳平台。在钨基 1L-TMD 中，低能量暗激子的存在对亮激子弛豫具有重要作用。然而，从亮激子到暗激子的详细弛豫动力学尚未得到充分揭示。在本文中，我们研究了单层 WSe _{2 中}自旋禁止暗激子的面外偏振光致发光 (PL) 的上升动力学. 在对亮 1s 激子共振激发的条件下，来自自旋禁止暗激子的 PL 具有几十皮秒的有限上升时间，这表明中间态，可能是热的间接暗激子，应该在从亮激子到自旋禁止的暗激子的弛豫路径。激发密度依赖性表明激子 - 激子散射应该促进自旋禁止的暗激子更快的弛豫。